so I'm 20 weeks and all the sudden today I've gotten sharp constant pain shooting from my belly…

so I'm 20 weeks and all the sudden today I've gotten sharp constant pain shooting from my belly button down into my vagina. so bad that it hurts to move, it hurts to walk, and has had me close to tears. my son is very low I mean... extremely low, he has been the whole time and he is still moving around. any one else experience this? I wonder if he's just growing or stretching my uterus or what.