I've Been Experiencing Quite Sharp Pains In My Lower Abdomen

I've been experiencing quite sharp pains in my lower abdomen that have only started today and I'm confused as I've never felt anything like this before. its a bit like pins and needles but like 10 needles being stabbed along the area at once.
I'm female, 21, having unprotected sex with my partner and have just received my period again today, but I think its about a week late but pregnancy tests have shown negative.