Perhaps she is actually pregnant, but not as far along as she says/it seems...so because she wanted to make a big announcement at the VMA's, she wore a prosthetic belly to exaggerate the pregnancy for effect? Then, because she got herself into this...she's going to continue faking it until she 'grows into it'?
That is what I think.
The pic does look really odd though and none of the theories offered in this thread really make sense imo. If it was the dress riding up over the bump, the 'lopsided bump' would be bigger than it is as it would be material AND the bump, when in fact it looks smaller.