Hi! Welcome to SP!
You've done great to lose 20 lbs. on your own!
Motivation is a problem, I agree. I find that reminding myself every day about how much healthier I'll be when I reach my goal weight is the best motivation for me. I have lost close to 20 pounds also (actually I had lost more, but I have had a lot on knee pain for the past two months and hadn't been exercising, so I gained about 10 pounds back again!!) But then I really noticed that I wasn't feeling as well - less energy, less flexibility, etc. so I'm back on track and starting to lose again.
I'd suggest you read at least a couple of articles a day, and/or blogs - that really helps motivate us. Also, if you can, make your page public, so people can visit you and support you. Posting on the message boards is another good way to meet people and make friends.