With each of my pregnancies I have felt what feels like the "warning cramps" of the period and it happens on and off for the first couple of months. What you are experiencing is normal. Take a panadol for the pain and try not to worry. If you are really concerned go and see your doc for reassurance.

BTW - This time around I had a lot of discomfort in particular on my right side and I now know that this is where the placenta is so maybe that's why I had pain there...