What is my body shape?

I have a small bust line and a large waist line. Buying clothes is very, very frustrating. I also have short legs, and chubby knees and ankles. The only thing that I feel comfortable in is pajama pants and oversized tee-shirts. I have a black tie event I have to go to in three weeks and I have no idea what to look for in a dress. Everything shows all my lumps and makes me look pregnant. HELP! Also I'm a size 22. Please no nasty comments, I really need some useful advice. Thanks in advance!