Cramps like crazy, but no actual period?

So I've been having cramps like crazy over the past week but I've never actually had a period. This is the third time they've been irregular and it's getting annoying. I had a blood pregnancy test done last time and it ended up being negative, so I'm wondering, what gives? Been a while since we "did it" too. I've also gained weight due to poor eating habits so I'm sure that plays a part in it. Thanks!