are u on a reset?

I can't see your diary, and I don't think I seen any posts from you on here about where your at and what you used to do.. But its not uncommon if you lost a ton of weight doing very low calories to suddenly start gaining weight.. Now 10 lbs in a month.. that might be a bit much (water weight, bloating, etc etc) but why not post a breakdown of what your following and what your stats are?
(So height/weight/age, BMR, TDEE, What your eating currently, activity level)

You already got some very good advice.

Everybody is different, and everybody does gain differently. I know hoe frustrating it can be, but you have to have to long haul in mind. You did not become overweight in a short time span. And if you want to do it right, you wont be losing it in a short time either.

The reset is a mind game and it can be really hard. But stay strong and hang in there. Once your body has realized what is happening it will stop storing every morsel of food. I can not tell you when you will stop gaining, but I am telling you to keep going.

Moderate exercise:
(typical week…sometimes I’ll switch up the days, but never work same body part back to back):

Mon: Weightlifting (Heavy) Lower Body A: 40 mins
Tues: Weightlifting (Heavy) Upper Body A: 40 mins
Wed: Pilates/Yoga/Walking: 30-40 mins
Thurs: Weightlifting (Heavy) Lower Body B: 40 mins
Fri: Weightlifting (Heavy) Upper Body B: 40 mins
Sat: Walking/Yoga/Pilates – some sort of movement 40-60 mins
Sun: Complete Rest

I’ve been trying to get a better night sleep but still find myself only catching 5 hours most of the time. Need to work on that.

Currently with my 10 lb weight gain, I have also gone from a comfy size 8 to a barely-buttoned 10 and slowly creeping to a 12. I’m afraid to go that far, so have been living in leggings, tights, dresses, and such items that don’t have anything to do with denim.

Good program.
So lack of protein could have some impact, but probably enough anyway when going by grams. Sleep can be pretty big factor actually if you show any signs of lack of sleep.

So I would suggest that your actually time at that activity is a BMR multiplier of 1.38, if rest of your workweek is sedentary level.
If your job or day is actually on your feet moving somewhat, that would raise that level depending on how long.

Lifting just doesn't burn the same calories as 40 min of cardio for instance, so you should eat less. It may indeed burn more during recovery for 24 hrs, but that is fat burn, and why replenish fat stores?
And the walking, yoga, pilates just isn't a big burn either, and mainly fat during the workout.

So weekly 160 min lifting, I split the difference of 50 min light cardio yoga/pilates, 50 min moderate cardio for walking 3.5 mph.
So while that is 4.33 hrs weekly, the intensity just doesn't deserve Moderate level in that 1919 study table for TDEE.

This is using the spreadsheet of course.

Not enough of correct stats to estimate BF% though, and you don't mention it. That could easily be a difference of 100-300 between BMR estimates of accurate and inflated if you can estimate your BF%.

Mifflin BMR - 1412 (probably inflated until you know your BF%, but may be avg and expected too)
TDEE - 1944 (based on above 1.38 multiplier)
Deficit - since you are doing an excellent routine of heavy lifting the whole body, and minimal cardio that could chance breaking down muscle, you could easily take a steeper deficit and maintain muscle and LBM. Studies have shown women taking 50-60% deficits and maintaining LBM and RMR levels. But that extreme is terrible for maintaining later, and they are under strict supervision.
So if you want fat loss and maintain current LBM/muscle, you could take a 25% deficit.
If you want to possibly increase LBM (not likely muscle though with a deficit and doing the lifting already), take the 15%.
So eating goal would be 1463 everyday with steeper deficit.

Your lifting probably burns 130 calories during the 40 min session. The most active walking level 3.5 mph for 60 min would burn 300 calories for your weight. The yoga/pilates less than that.
But, remove the already accounted for TDEE of 1944, or 54 cal for 40 min, 81 cal for 60 min.
So lifting burns 76 calories over and above what the TDEE had you burning anyway, and walking cardio is 219 calories.

So while that goal looks close to BMR, the weekly avg is fine.
Or just use those calorie counts and NET above BMR if desired. Or take the 15% deficit and no worry about it at all because you'll have a much bigger buffer anyway.

So you have stopped gaining at this point, mainly during the initial increase of calories?
Or still gaining that would seem to indicate eating over TDEE?

Because 1 month for 10 lbs is pretty good gain. Even if you count initial 4-5 lbs water weight. You haven't gained muscle in that time as your BMR must have been suppressed, and your body isn't going to build muscle if still suppressed. Other LBM mass including water sure, not muscle.

Moderate exercise:
(typical week…sometimes I’ll switch up the days, but never work same body part back to back):

Mon: Weightlifting (Heavy) Lower Body A: 40 mins
Tues: Weightlifting (Heavy) Upper Body A: 40 mins
Wed: Pilates/Yoga/Walking: 30-40 mins
Thurs: Weightlifting (Heavy) Lower Body B: 40 mins
Fri: Weightlifting (Heavy) Upper Body B: 40 mins
Sat: Walking/Yoga/Pilates – some sort of movement 40-60 mins
Sun: Complete Rest

I’ve been trying to get a better night sleep but still find myself only catching 5 hours most of the time. Need to work on that.

Currently with my 10 lb weight gain, I have also gone from a comfy size 8 to a barely-buttoned 10 and slowly creeping to a 12. I’m afraid to go that far, so have been living in leggings, tights, dresses, and such items that don’t have anything to do with denim.

Good program.
So lack of protein could have some impact, but probably enough anyway when going by grams. Sleep can be pretty big factor actually if you show any signs of lack of sleep.

So I would suggest that your actually time at that activity is a BMR multiplier of 1.38, if rest of your workweek is sedentary level.
If your job or day is actually on your feet moving somewhat, that would raise that level depending on how long.

Lifting just doesn't burn the same calories as 40 min of cardio for instance, so you should eat less. It may indeed burn more during recovery for 24 hrs, but that is fat burn, and why replenish fat stores?
And the walking, yoga, pilates just isn't a big burn either, and mainly fat during the workout.

So weekly 160 min lifting, I split the difference of 50 min light cardio yoga/pilates, 50 min moderate cardio for walking 3.5 mph.
So while that is 4.33 hrs weekly, the intensity just doesn't deserve Moderate level in that 1919 study table for TDEE.

This is using the spreadsheet of course.

Not enough of correct stats to estimate BF% though, and you don't mention it. That could easily be a difference of 100-300 between BMR estimates of accurate and inflated if you can estimate your BF%.

Mifflin BMR - 1412 (probably inflated until you know your BF%, but may be avg and expected too)
TDEE - 1944 (based on above 1.38 multiplier)
Deficit - since you are doing an excellent routine of heavy lifting the whole body, and minimal cardio that could chance breaking down muscle, you could easily take a steeper deficit and maintain muscle and LBM. Studies have shown women taking 50-60% deficits and maintaining LBM and RMR levels. But that extreme is terrible for maintaining later, and they are under strict supervision.
So if you want fat loss and maintain current LBM/muscle, you could take a 25% deficit.
If you want to possibly increase LBM (not likely muscle though with a deficit and doing the lifting already), take the 15%.
So eating goal would be 1463 everyday with steeper deficit.

Your lifting probably burns 130 calories during the 40 min session. The most active walking level 3.5 mph for 60 min would burn 300 calories for your weight. The yoga/pilates less than that.
But, remove the already accounted for TDEE of 1944, or 54 cal for 40 min, 81 cal for 60 min.
So lifting burns 76 calories over and above what the TDEE had you burning anyway, and walking cardio is 219 calories.

So while that goal looks close to BMR, the weekly avg is fine.
Or just use those calorie counts and NET above BMR if desired. Or take the 15% deficit and no worry about it at all because you'll have a much bigger buffer anyway.

So you have stopped gaining at this point, mainly during the initial increase of calories?
Or still gaining that would seem to indicate eating over TDEE?

Because 1 month for 10 lbs is pretty good gain. Even if you count initial 4-5 lbs water weight. You haven't gained muscle in that time as your BMR must have been suppressed, and your body isn't going to build muscle if still suppressed. Other LBM mass including water sure, not muscle.

Another great read. Thanks Heybales for another good insight!