Sounds like a Braxton Hicks to me! It's basically your uterus "practising" contractions, they shouldn't really hurt as such (although for some people they do), more just a tightening of the muscle. I think they can start around the middle/end of 2nd tri or not until you are in 3rd tri but like most pregnancy things everyone is different! I only ever got a few and they weren't super noticeable, just sometimes my tummy would feel tighter than normal.