Hang in there, Shawna777. Please see a therapist who specializes in transgender issues, even if they are in the next town. (If you aren't already.)
You are correct, these feelings don't go away. In fact they tend to get more intense with age. I got quite overweight more than once, and now I know why- being overweight drops testosterone and increases estrogen levels. Transgender brains have too many of the wrong hormone receptors for what your body produces. I ended up in therapy after I had lost a significant amount of weight, which sent my dysphoria (and drinking) into overdrive. I was shocked when she told me I needed to get on a low dose of estrogen immediately. I didn't want to be trans, nor did I want to deal with transitioning socially. I hoped on some level that estrogen wouldn't do a thing for me and that she was wrong. Two hours after my first dose I felt the best I had felt mentally since I was about 12 and I went full time a few weeks later, came out to the world and never looked back. Estrogen made me feel better than all the drugs I ever did, and I refuse to go a day without it.
And don't worry about your big frame. I'm 6'2" and built like a linebacker, but I'm still seen by most as unmistakeably female. There's lots of cute cisamazons out there too.