I was in the same boat as u....
Hypothyroidism - Hashimoto's Disease. I had a large goiter in my thyroid and had half of it removed. Luckily no cancer. I am on Synthroid at same dose as you and take Zoloft 50 to 100 mgs per day.
I had some bruising, and was major fatigued for almost a year after starting the Synthroid. I think it takes a while for your body to process the replacement hormone correctly.
I had always been a cardio freak but that did nothing to help my weight gain.
The answer was weights & diet. No dairy, very little processed food, only water to drink. Drink over a gallon a day. And I have my body back - much better than it ever has been.