Negative Pregnancy Test, Stomach Cramps

Erin
I've been off The Pill for a month now, we had sex in my ovulation days, and I was supposed to have my period a week ago. All the tests I've taken have been negative, but I've had sore boobs, been extremely tired, and just recently my stomach had been cramping sooooo bad. It hurts in my stomach and deep in my lower back. Anyone had a similar experience??? TIA