Is this normal for my cup size to change so much? Up until i was 16 i was a B cup then when i turned 17 i went up to a C cup for a couple of months. Then they dropped back down to a B a couple of months later. I decided to measure myself recently and from the instructions it now says im an AA cup because my back size is 28inches plus the 4 makes it 32 and my bust size is 31 which makes me an AA cup. I enjoy swimming, and i go swim 3 times a week for an hr or so. Do you think this has anything to do with my decrease in bust? I started swimming when i was 16 though. I'm very petite in figure but that has to do with genetics than anything else.