I'm getting cramps & back pain. Implantation?

I started to ovulate on the 15th February and my most fertile day was on the 17th of February. I had unprotected sex on the 17th and my last fertile day was the 21st (yesterday). Today when iv been at work iv been getting light cramping. Someone said to me that it could be ovulation pains but it's starting to feel like a period type cramp it's a medium cramp and it's in my back also. Could this be implantation?