I had always been 160 lbs since 8th grade, which was a fine weigh...

I had always been 160 lbs since 8th grade, which was a fine weight for me bacause I'm tall and muscular. When I was 25 I gained 20 lbs over 3 months with no change in diet or activity. So I went to the doctor because hypothyroidism is very prevelent in my family. The blood work showed I was borderline hypothyroid, so the dr didn't suggest starting any medication. So I started working out 4-5 times a week for at least 1-1 1/2 hours per day. I also got on phentermine to help jump start my diet. After doing this for 2 months, I had gained 5 lbs. Which is crazy because anytime I needed to lose weight, I had no problem dropping 10 lbs in 2 weeks. I was frustrated but ignored it for a while because I got pregnant shortly after that. During the pregnancy, my throid was checked again and was normal. I weighed 248 lbs the day I went in to give birth. 2 weeks later, I weighed 210lbs and a month after that I was 200lbs. Then I went back to work,(where I walk continuously all day) and I could not budge my weight below 200 lbs no matter what I did. So I went back to the dr and I was slightly hypothyroid again. I opted to go on generic Synthroid 25mcg. I then gained 37 lbs over 4-5 months. So I went to another dr. to get on phentermine. I started the phentermine and lost about 27 lbs. I have been off phentermine for a while, but have been working out vigorously working out and watching my diet and couldn't lose another pound. So, I thought the synthroid might be making it harder to lose weight. I stopped taking it and have lost about 10lbs in the last month. I think there is definitely a connection in synthroid and my inability to lose weight. But I still can't get below 200lbs and I still feel sluggish. I am only 28 and don't think I should attribute this to age. I can understand age causing weight gain of 5-10 lbs per year but not 155lbs in May '05 to 183lbs in Nov '05 then to 200lbs in Jul '07. Please give me any suggestions you might have. Diet, medication, activities???