Obviously there are a number of possible contributors to weight issues; knowing that you have had a thyroid problem for quite some time, and also knowing that most doctors don't seem to adequately test and treat hypothyroid patients, I would be suspicious that you are under medicated. In which case your metabolism is affected and it becomes very difficult to lose and maintain weight loss. So please post your thyroid related test results and reference ranges shown on the lab report.
Have you had your levels checked lately?