irregular period problem..HELP!!

Okay so I've been to multiple doctors about my irregular periods. It started a couple years ago, I went about 5 months with out a period and my doctor said it was just stress from school. Eventually they went back to normal. About 6 months later they went back to being irregular and I only get one about every other month now, but I never know when it's coming. I've had blood tests done and ultrasounds. Everything seems normal. When i do finally get a period, it makes me super sick and I have really painful cramps. I really need to find out what could be wrong because I'm getting married in September and then I will be ttc and I need to get this solved before then to make the process a little easier. Has anyone ever experienced anything like this or know what it could maybe be? I made an appointment with a different doctor but I can't get in for a while. Thanks!