DE, I have been trying to tell drs. since I was 15 y/o (I'm now 41) that I have a thyroid problem. Every female in my immediate family -- mom and all 3 sisters -- are hypothyroid. I would get tested, and they would say, "oh, it's low, but it's LOW NORMAL" and pat me on the head and send me home, as you've described.
My pdoc, when he did the bloodwork that found the aplastic anemia last year, did thryoid function tests too. At last, it came back SO low that there was no denying it was abnormal. Synthroid got it back up pretty quick, but I had such trouble being compliant with it that I quit it. We'll see what my new internist says about that when I see him on the 1st.
I can't say having a regulated thyroid helped my depression either, but I do SO relate to drs. blowing you off. I hope things get better for you.
Love, Candy