My BH's have been much more full on with this pregnancy - my belly gets achy and I feel it pulling around to my back. They've got more frequent in the last two weeks as well, but I haven't needed to take pain relief though. I remember distinctly the sharp pain of labour contractions so I know that's not what they are but I can understand why it would freak you out if that bad.
Try to take it easy for a few days perhaps you're overdoing it, I know I have been.