tmi .. but had some "me time" and afterwards my lower belly got super hard and it felt like it was being pushed against?…

tmi .. but had some "me time" and afterwards my lower belly got super hard and it felt like it was being pushed against? then went away after like 30 seconds? but its weird cause after sex with my bf I don't think I've noticed it... maybe it goes away too fast for me to notice, cause afterwards I'm usually like out of breath just focusing on catching it lol . this ever happen to you?