Pain After Sex?!

Sunshine
So last night, me and my husband had sex missionary style (he does this a lot with me cause he loves it) and after we both finished, maybe 5 minutes later, I started to get this pain like if I was about to start off my period. So I got up and put panties and a liner just in case. I was in much pain, it wasn't cramps, it was something else. It took me about 30 minutes to fall asleep cause it kept me awake. Mind you, we do this position a lot and this is the first time I've ever had pain after sex. According to Glow I was due for my period yesterday but it never came. The day before I took a test with FMU which came back negative. I have gotten tested maybe a few months earlier and I don't have fibroids or cysts, no UTI and no STD. I was very wet (sorry tmi) so I didn't have friction from dryness... What's going on? Oh, and for about 3 or 4 days I had a lot of stretchy and clear mucus a few days ago so not sure what's going on... Help please!