Cramping after sex?

First time TTC, first fertile window is going on now, and today is day 2. Since this is so brand new for us, my husband and I are just kind of going with the flow for now to see what happens, and I'm not really tracking anything other than dates of AF and keeping track of when we have relations. Like I said, today is day 2 of my fertile window per the calendar on this app and after BD this evening, I've had some cramping, which is new for me. I have no clue what that could mean. Any thoughts or suggestions?