Cramping 1dpo

Paige • 23- UK. Our little pea due November2017 ❤🌈🌞
My last fertile day was yesterday. We only had sex once in my fertile window which was 3 days into my ovulation days. I'm at work at the minute and I'm starting to get really bad cramp. Does anyone have any ideas on what this could be? Is it too early for implantation?