I had the same issue around the same time as you. I didn't think anything of it really. Just the fact that my baby was growing inside me and everything is shifting to make room for him. I'm now 22 weeks and i don't have that pain or pressure anymore. I think it could be a phase that the body goes thru when the baby grows. Mine went away after week 15. Just take it easy til it goes away. If it really bothers you then ask your doctor next time you go in or give them a call.
This literally happened to me this morning , I thought it was a full bladder at first but it wasn't. Someone told me its your ligaments , nothing to really be worried about .
Everything is stretching and moving and growing to accommodate the baby. If it's not severe pain or anything like that I wouldn't be too worried about it.
Thanks girls!! Thats eased my mind:)