Frustrated and losing hope

For the last year my husband and I have been TTC. After taking a PT and getting a BFN, In my heart i know there is something wrong with my reproductive system. I am overweight and I do have a thyroid problem. I have been trying to lose weight but the doctors can't seem to stabilize my thyroid. Every time I ask about fertility, the doctor just says that it's because I'm overweight and my thyroid issue. But I know other heavier women who got pregnant without any issues. I am frustrated, depressed and now losing hope.