i dont know if this has anything to do with it but when i was 12 weeks pregnant i used to see a bumb in one side and then it went down, at 13 weeks it happened almost every morning and in other times of the day (and it always happens when i had sex and it still happens), most of the time it was on the left side, like if i had a tennis ball or something in there, when i got further along (about 16 weeks) it still happend and i felt movment there so it was the baby all along but it started to happened on the right side and on the middle too. im 27 weeks 5 days now and it still happens but the bump is much bigger now and then goes down.
i dont know if this may be the same thing that is happening to you, but if your concerned talk to your dr.
If you are very concerned then you should mention it to your doctor. At 16 weeks is when I started to notice that my belly was starting to stick out more. It could be your uterus or just the way everything is shifting. All of your organs shift up in order to make room for your baby and depending on your body type will depend on how, when and where everything goes.