Having been overweight for almost my entire life, it has been a challenge. A lot of great advice here! I too, have struggled with seeing my body for what it really looks like now, as opposed to what it USED to look like. This happened just again yesterday. I needed to buy a nice dress for an upcoming fundraiser and ended up at a bridal shop. A consultant there picked out a dress that I would have never thought to try and it looked fabulous on me. I had on a size six and I was like "It fits perfect!" She came up behind me, grabbed the excess fabric behind my back and was like "No, you actually need a size four." Sure enough, the size four fit like a glove, even though I was convinced it would never zip.
One thing that I will say that has at least helped with the "being convinced I am beautiful" issue: If you haven't tried yoga, I highly recommend it. There is something very grounding that comes with increased body-consciousness. When I focus on what my body can do, and not just what it looks like, I feel particularly good about myself.