This is just a guess if your gaining at 2100 calories and your lifting 3 times a week then either your activity level isn't correct.That's my guess i would do a 15% cut from that 2100 and make sure your not netting under your bmr.

I ran your numbers through scooby and it says your bmr 1459.Your tdee for moderate activity is 2262 your calorie intake with a 15% cut is 1922.For light activity tdee 2006 calorie intake 1705 with a 15% cut. I would again just a guess 1922 and you wont have to eat exercise calories as long as your not under 1459.

I would start the cut process as well and 1900 is a good number to start at. I also can't see your diary, but make sure you adjust your macro's so your eating enough protein as well as carbs/fat.. To make it easy try to eat your weight in protein, so 155 and adjust your macro's to meet that.. just a suggestion.

After sticking to a 1200 cal diet for most of a year (partly the result of low self-esteem from divorce), I have basically been resetting since July. So it's been about five months, with a 3-week cut break about a month ago. My cals have stayed at about 2100.
When I cut for three weeks in Oct. I was at 1800--it wasn't long enough for me to notice anything.

Then I got my BMF, and after a month I see that my TDEE is 2300. I redid my numbers on heybales' spreadsheet, and that comes out to 2300 as does Scooby.

It seems that I am still slowly gaining weight at 2100. I don't weigh, but I have measured all along. And my clothes are tighter and tighter.
If it's been five months, am I done with reset? I am so tempted to go down to 1500 right now.

So the BMF bases calorie burn on a foundation of your BMR, age, weight, height - the Harris formula.

In the spreadsheet, TDEE deficit tab, how much difference is there between most accurate Katch BMR and Harris BMR?
You may be getting inflated burn values from the BMF if the foundation of the calculations is 200-300 off, which I've seen many times.

About 45% BF will cause 200 easy.

Do you know how much you have gained during the reset for like a 3 wk period of time? And was it about equal each week?
And what was avg eating level during that same time, daily?
We can calculate your exact TDEE from those 2 numbers if you were just flat out gaining because of eating above TDEE.

Do you think you might be underestimating your caloric intake? (IOW, how truly accurate are your food numbers - do you count every bite?) And what kinds of foods are you eating? (What are your macros?) Are you getting enough protein?

Over the past three weeks I am guessing I've gained about three pounds. About 2 inches in both my thighs and butt. With all my weightlifting, it's hard to tell in terms of lbs.

Ok, so good to know the BMF TDEE estimate is going to be mighty close than barring any thyroid issues.

To this point though.

1 lb a week, if only fat gain.

Eating at imagined TDEE, and eating 500 more. Daily. For 3 weeks.

So if you think it was fat gain because of increased size, do you really think the TDEE is 500 lower?

I'll bet you gained LBM, if not a smidgen of muscle. And more LBM, even if no muscle, means increased metabolism to care for it.

Have you had a flush effect? Do you drink?
http://www.leangains.com/search/label/Water Retention

What is your carb macro set to? Do you go consistently over it even after logging exercise? Our macros can be the most important thing sometimes, esp if we don't pay close attention to carbs. I'll wait for your answer before explaining why I asked... No point getting an essay from me if it's not gonna help!

I'll try and keep it short.

You eat carbs, and they are converted and stored in the muscles and the liver. Your brain & muscles use them for fuel, but the muscles and the liver can only store so much. The bottom line, if you eat over what the muscles/liver/brain can use or store, they are converted to fat. I am sure this is something you have heard before.

Thus, the more carbs you eat (especially high-GI), the more insulin released into your blood to combat the rise in sugar, and then this signals your body to store more fat.

You can have a bit of a read here: http://www.naturaltherapypages.com.au/article/Insulin_Weight_Loss

I wonder if it's worth trying to raise your protein significantly and lower your carbs a bit over the next couple of weeks just to see. By no means cut out carbs completely, but just see if you can stick slightly under your 40%, and go over with your protein instead. I know for me, especially with my family history, my best weeks are the ones where I keep my carbs most in check. I seem to get much better results. I have been insulin-sensitive all my life and have been known to put on fat very quickly just from a couple of really bad carb weeks, even if my calories are in line.

I know what you've said about struggling with protein, but it might just be your best friend here so don't give up. I know plenty of vegetarians that are hitting at LEAST 30% protein every day, I see their diaries. It just needs a bit of research. I think your 50% carbs is definitely too much. Also, if you log exercise as cals burned, it also adds value to your carb macro as well, meaning you're eating even more carbs when you shouldn't be. This is because MFP is designed to be set at a low level, then eat exercise calories back. It doesn't account for those of us that follow the TDEE/cut method.

Bottom line.... I honestly think that carbs are the missing link in a LOT of people's struggles where calories in/calories out just doesn't seem to cut it.