Help - did I kill my metabolism??

Hi everyone, I just registered for the sake of posting here so I don't have a diary or anything yet; I hope I can still get some insight or advice. Please be kind I know some may think I'm being silly here but I'm really concerned, so I would appreciate no mockery or insults. Sorry for the super-long ramblings )

So I guess my story begins back at around puberty, where I suddenly gained some weight after always having been a skinny kid. Not much - I was about 120-125 lbs at 5'4 from about 16 to 23 - but I'm very small-boned (my wrists are ridiculously tiny) and I've never been very athletic so on me, it looked chubby. During those years I tried all the usual stuff to lose weight - different eating plans, calorie counting, gym, I never did anything crazy restrictive but I was typically eating around 1000-1200 calories, working out several times a week (cardio and machines as was the norm for women back then), and the weight wouldn't budge. By about 24, I've gotten down to 118, which I could maintain without a very strict diet, and I sort of accepted that that was my body's set weight below which I wouldn't be able to get, and I was more or less okay with it even though I still would've liked to lose 3-5 more lbs.

Well, lo and behold - something happened around the time I was 25. I still don't know what - I might've been eating slightly less than before, but it couldn't have been that much, I didn't change much at all - but in less than a year, I lost 10 lbs without even realizing it. Literally - I went to the doctor and was shocked when I stepped on the scale and it showed 108! (I didn't own a scale back then). Only then did I notice that I did actually look so much better and thinner. I LOVED myself at that weight. I thought I looked fantastic, for the first time in years. The biggest change was my face - I never realized before how much of those 10-15 lbs were in my face and how much prettier I looked once they were gone!

I stayed around 110 lbs for the last six years. I got pregnant and gave birth, going back to 115 right after and back to 110 once I stopped nursing. I did some cardio all this time but didn't really watch what I ate - I just didn't eat much. When I did count my calories out of curiosity for a bit, i would average between 800-1100, maybe going up to 1400-1500 on special occasions. I wasn't starving myself - my stomach must've shrunk and I was almost never hungry and didn't want to eat more, when I did I'd feel uncomfortably full for hours. I also stopped watching WHAT I ate - once I realized I could eat whatever I want as long as I don't eat much, and I wouldn't gain weight, it was just sooo incredibly liberating after years of 'dieting'! Gradually, I started replacing healthy foods with foods I felt like eating; I didn't feel like eating meat or veggies, so I didn't. I was fooling myself - saying I was 'listening to my body', 'eating when I'm hungry', 'eating whatever I want in moderation', 'eating all natural foods' (that was semi true, I at least stayed away from artificial junk like fast food, soda, chips, etc), 'eating like the French do'...in reality, what that was translating to is I could go the whole day eating nothing but coffee, baguette, yogurt, and chocolate, and feeling like I was being sophisticated and refined. Looking back, what I was really doing is abusing my body but I was staying skinny so that's all that mattered.

Now, I've had a problem with low energy and excessive fatigue pretty much all my life; so had my mom and grandma so I didn't think much of it. I've gone to doctors and had all bloodwork done several times and nothing was ever found to be wrong. In the last year or so, though, I felt it's gotten worse. I was exhausted all the time, couldn't keep up with my son, was cranky and irritable, and wanted to spend every minute in bed. I thought it might be related to my poor diet and tried eating better but never had the willpower to keep with it and would quickly go to my old ways of fueling with caffeine and simple carbs. I also started to get other hormonal symptoms, like less regular cycles and terrible PMS. Finally I decided to see an endocrinologist. I had my bloodwork done yet again - and it showed my TSH at 4.37 - up from the 2.4 it had always been before. The endo wasn't concerned though - she basically told me it's not high enough to be responsible for my symptoms, and gave me a prescription for Synthroid but told me it was up to me if I wanted to try it, but to not be surprised if my symptoms don't improve.

That was about three months ago. Since then, I've tried making some changes in my diet, cutting out the empty calories and replacing with meat, eggs, fruit and veggies. I've also started doing squats, lunges, and deadlifts to tighten up my skinny-fat pear shape. In those two-three months, without eating more calories (and I'm certain of it, even without tracking, I've been eating less if anything), I've gained two pounds - went up from 110 to 111 last month and 112 this month. I know. it's only two pounds. It's not much. But after I've been maintaining 109-110 lbs for five! years without watching what I ate - and that includes vacations, holidays, restaurants, months of no working out, eating a lot more junk food, sugar, bread, etc, it's now really freaking me out because I'm afraid it's related to the thyroid. I got the Synthroid but I haven't started taking it and I don't know if I should. I've been doing tons of research since, and read so many horror stories of women gaining crazy amounts of weight on synthroid in spite of eating very little, it's terrifying me. The idea of uncontrollable weight gain is seriously one of the scariest things for me.

I was also reading a lot about the effects of long-term calorie restriction, and though I've read on these boards that starvation mode is a myth, I've also read other accounts of people who experienced 'metabolic injury' as a result of long-term undereating and/or overexercising. I also found a study that demonstrated a temporary reduction in thyroid function as a result of protein malnutrition - and I definitely hadn't been good about getting my protein. Yet I've also read that actual hypothyroid causes a lower RMR hence you need to eat less to avoid gaining..

So now I'm stuck. I'm frozen in fear of gaining more weight one way or another. I have no idea if my thyroid slowed down on its own, hence I'm gaining weight and I need to eat less...or whether I might've actually CAUSED the thyroid slowdown due to years of not eating properly, and therefore maybe eating MORE, of good-quality foods and more protein, might help to actually reverse it? Or maybe the two pounds is just water from starting weights (I'm seeing a slight difference in the way my legs look but no fat has been lost off them) and I'm freaking out for no reason? Could water weight be responsible for a pound of month of weight gain? I'm lost, I really don't know. I should mention even though my weight was low all these years, I've still always had fat on my legs, hips, and love handles while my upper body is extremely skinny, and my bf has been measured around 20%, though not sure how accurate that was (electrodes at gym). So ideally I'd like to lose some fat and build muscle...but I'm also afraid to eat more, because what if I DO have actual thyroid issues and will only gain more weight?? I have a small frame like I said, so every pound is very noticeable on me. I'm also afraid of starting synthroid as I've read so much about weight gain with it...but I'm also afraid of thyroid going even more hypo if I don't...I just don't know, and the endo hasn't been helpful at all. I'm so scared of putting the weight back on, I look at my old pictures and I can't go back to that (( Maybe anyone has had any experience with this - help????