Very heavy feeling in uterus - pregnant?

Hi everyone, I am 20 weeks pregnant and for the past week or so I've been having this heavy feeling on the left side of my vagina area..I literally feel like the baby' foot is jammed in there or something! It usually happens in the morning when I wake up, sometimes it is so heavy that I have to actually try and push whatever it is back "up" and it goes away, but it'll come back again sometime throughout the day at least once! Its starting to scare me a little and my next prenatal visit is on June 12 when my GYN gets back from vacation :/ -- I've called her but she needs to check me because she's not sure..I just wanted to know if anyone else has had this experience before? My daughter (first born) is 7 months, could this have anything to do with it? My GYN says baby is low and I misscarried back in 2009, I'm not sure if any of this helps, I just need some answers...thanks!