Fluttering in stomach post SEX lol

So has this happened to anyone else? So a few months ago in February I didn’t take a plan b pill. After the pill I did get my period and everything was fine. Now we’re in may no I have not missed any periods, and I’ve taken 2 pregnancy tests since Feb and both negative. but the last few times after sexual intercourse I had alot of fluttering in my stomach for about 2 hours after the sex. I have 1 child already so I know what fluttering feels like from pregnancy and it’s pretty damn close. This has me confused af?!?! Please reply on what u all think?