What are your latest labs? TSH, Free T3, Free T4?
I am feeling a similar experience as you.
Weight gain can be due to a number of different things. One of those is, of course, being hypothyroid. Since you apparently have been previously diagnosed as hypo, and are taking meds, that makes me wonder if you are adequately medicated. If the thyroid hormone levels are too low in the range, that can cause hypo symptoms, including low metabolism. If your metabolism is too low for your weight, age and height, then it becomes a Herculean task to lose weight and maintain the loss.
If you will please post your thyroid related test results and reference ranges shown on the lab report, members can assess the adequacy of your testing and treatment.