why am I gaining weight??

Are you weighing your solids and measuring your liquids???

How many shakes a day were you consuming?

How do you measure you calorie burns? and what kind of exercise is it?

Just to clarify, have you not seen any loss from the increased 13lbs when you changed over, or are losing from there?

ETA if you open your diary it might help too

If you have dropped 100 pounds in weight then your BMR has changed substantially and any workouts you do are burning likely less calories as well unless you have increased their intensity.

That said it does seem unlikely that you would put on fat weight (if that's where that weight comes from) at just 1450 cal a day while also working out.

I don't know how long it took you to put on 13 pounds but its possible by eating more and eating solid foods you stopped from burning up both fat and muscle on your shake diet to actually putting on some muscle on the new diet.

So have you noticed any change in your waist size when you put on this 13 pounds?

Also...800 calories in a single workout? That seems really...really...really high. I do 55 min of heavy aerobic cardio as a 6' tall man and I think I burn about 400 cal doing that.

You mean you eat 1450 calories NET right, taking into account the amount you burn during workout. You aren't just eating 1450 calories AND working out hard on top of that without eating it back right because really that is just going to hurt you.

Also I'm pretty sure anything that measures calories burned like polar watches do it on top of your BMR. Meaning if you work out for an hour and it reads 400 cal burned but then you wear it for an hour sitting on the couch and it reads you burned 200 cal then really your workout only burned 200 calories extra past your BMR level.

Have your measurements changed? Are your cloths tighter?

I don't mean to alarm or be rude but if you ate only 1200 calories a day for 1 year while simultaneously burning ~800 calories a day with exercise for 5 days a week that means that in a week you net just 3400 calories or an average of 486 calories a day. That is starving yourself plain and simple. You will lose weight rapidly doing that sure but that weight will be both fat AND muscle AND bone density. You will drop weight but you will also become weaker, your metabolism will slow, you will have less energy (although that loss of energy might be somewhat masked by being lighter from the weight loss). Eventually you are going to burn yourself down to your essential muscle at which point your body will start to suffer from malnutrition and you can really harm yourself. Your body will literally start shutting down you will be extremely tired and your metabolism will drop through the floor as your body does what it can to hold onto any bit of fuel it can.

You aren't going to like this advice but really what you need to do is throw away the scale, eat more food, continue with light exercise and build a little muscle back...get back energy. You will put on weight but eventually that weight loss will slow as your metabolism revives and you put some muscle back and eventually you will resume weight loss once more at that elevated calorie level while having energy. Upping your calories and switching to whole foods is heading the right direction but really if you are only eating 1450 and working out that much you need to eat even more.

If I misunderstood and you mean you net 1200 a day and now net 1450 a day then that's okay.

How is your energy level though? Are you getting stronger from your workouts? Do you find yourself tired throughout the day?

At this point I would suggest going to see a Dr. You have been eating well below BMR for a good long while. There is no way you are putting on fat or muscle which means your body is retaining large amounts of water and that is not a good thing. Go see a Dr. or nutritionist, or both.

Yeah I agree with this. I had only suggested putting on muscle when I thought you were netting 1450 and that that was above your BMR. I don't think what you are doing is particularly healthy and you might want to consult your doctor on it if you haven't already. Get a physical, find out what your levels are and if you are malnourished.

You were under eating for 13 months, and then you raised calories, but still not enough to sustain the amount of energy you need. Maintenance should be more that 1450 calories. For an active young woman it should be over 2,000.

When you put stress on your body (including stress from diet and exercise) your body produces excess Cortisol which is a hormone. Raised cortisol levels over time can cause you to gain weight.

You may need to take a diet break to try to reset your body and get the hormones balanced, then take a reasonable deficit (to lose half a pound a week) to take off the 13 pounds you gained.