Feeling movements extremely low

Hi ladies.

I am 21 weeks along with twins. Twin A, on my left is sitting low and I have a partial placenta previa on that side as well. Lately, I’ve been feeling movements extremely low. So low it literally feels like they’re going to fall right out of my vagina. The movements have been right above my pubic bone and on my bikini line. These happen mainly when I am sitting down. When I lay down I feel both move near my belly button. Im going to call my doctor in the morning to ask him about it but wondering if anyone here has experienced this? Thanks!