Cramping after Working Out

I am freaking out because I'm 4 weeks pregnant. I'm the head volleyball coach at our high school and tonight I was tossing balls to the girls and serving. I felt a strain in my stomach (lower) and instantly was terrified. I am having slight cramping this evening and am horrified to miscarry because of something so stupid. Do you think I'm ok? So far no spotting or bleeding just cramping. Ugh will definitely lay off.