Cramping without bleeding.

I'm 5 weeks and this morning and I have a lot of cramping behind my pelvic bone. I know some discomfort is normal as the uterus is stretching and I've felt some cramps before but not like this. This is definitely more intense than a period cramp, but it's not constant, just sharp twinges that last a few seconds. There's been no bleeding though. Should I be worried? This is my first pregnancy so I'm freakibg out about every thing because I'm so afraid to experience a MC ?