Slight pelvic crampibg

Hello, I'm four weeks along and have been feeling slight cramps. They don't linger--it's more brief, then poof, gone.  It tends to be either sharp or slightly achy. I'm so paranoid with this being the first pregnancy, that it could be a possible miscarriage. I hate thinking of the worst--but I can't help it. Has anybody else been experiencing these pains?