Bonnie, cheaper bras DO stretch pretty quickly. And you're not that much shorter than me. At your weight, I was in a 36D.

Have you tried getting professionally fitted? When I went to Vicki's Secret, I was pretty sure, based on the instructions on the Soma site for measuring, that I needed a 32 band. But was shocked to need a DDD. I had her bring me a DD, just to see, but she was right: DDD it was and is.