I had them from about 36 weeks with my son although didn't really feel them very often until 38 weeks when they became quite frequent and stronger as time went on. During the last 2 weeks they were so strong sometimes I thought my labour was starting then they would go as quick as they had come! Not everyone feels them though, your body is just practising and warming up your uterus for labour, so it's all good. It can only be a good thing if you're not feeling them, but then if you do use them to practise your breathing and relaxation for the big day. I wouldn't worry if you don't feel them, but just keep an eye on your bump, you might notice it get harder and more tense every now and then, you can feel it with your hands even if you don't feel any pain.
Good luck!