My dr. told me that contractions have to be constant and that they hurt so bad that you would no be able to handle, so you will know when is time. He also said that your tummy is going to get harder..
Could be contractions. If they don't stop with change of activity, time them. Once they last 45 seconds and are happening every five minutes, go to the hospital. And just so you know, early labor can last for days with your first child, so if you need to get something for pain management or to help you sleep, don't be afraid to go to the hospital to get something.