painful cramps

I'm 4 weeks and 4 days pregnant for the last 5 days I have had cramps, I have read this is normal however they come and go and aren't here all the time, but they are very painful when they happen. The pain is in the middle of the bottom of my stomach not left or right. Has this happened to people? They only last 5-20 mins then disappear and I'm fine untill they happen again What was the outcome? Was baby fine?