Gas or Implantation Cramping?

I'm 6 door TTC #1 after a chemical miscarriage last October. We bd'ed every other day during my fertile week. Today when I woke up, I went to pee and started cramping like I was gonna start bleeding at any second. I've had lots of gas and some would say I'm constipated but since I'm not regular, I would say it's normal for me. The cramping only lasted about 15 minutes but boy was it intense... Could it be implantation cramping or is it safe to say it was gas that felt like menstrual cramps?