for me it was this horrible cramping feeling and then a shooting pain in my spine.
It's different for everyone, but what you really want to look out for is consistency in the contractions. Mine felt like a tightening and would take my breath away and also felt a little like period cramps or like I had to have a BM. But with me I had no clue I was actually in labor until my midwife checked me and I was 5-6cm. They didn't become painful for me until 8-9cm. Keep an eye on them and time them. You are just about there! =)