I had the same experience when I started doing squats. Don't even ask me about the yoga class that introduced me to my hip flexors!
(really you should've seen me try to move the next day, my abs were hurtin' too.)
I would say it's probably normal, if you keep at it for a couple weeks and keep stretching and doing your warmup/cooldown it should get better. In the mean time you can take some ibuprofen if you find it really bothersome. Hot baths in the evening (NOT immediately post workout) seem to help me as well.