I had these as well. I had to take magnesium citrate and vitamin D all month. Might have to add in calcium (at a different time than the mag) once the diarrhea hits. Once I got on the magnesium regimen I was so much better I couldn't believe it. It helps with muscle cramps and anxiety and pain.
Try taking a magnesium supplement.if you are already on calcium supplements they usually come in combination with vitamin d and magnesium. Maybe also consider having a blood test so that your doctor can see what's lacking in your diet
I get bad cramps as well. Ibuprofen usually helps a little, I have recently found that rubbing a little magnesium oil on your stomach is helpful as well. I ordered mine on amazon, but you may be able to find it at a local store as well.
My answer may not be all that helpful, because I don't know what you can do other than try birth control or getting yourself checked out by a doctor. And if your doctor says it's normal, find another doctor because debilitating cramps aren't normal. I, myself have cramps that can be so bad that I faint from the pain. I'm going to the doctor's on Tuesday, myself, to see what's wrong. My mom suspects ovarian and uterine cysts (like she had when she was my age (16) and up until she had her first child.) Only difference with my mom and I are that mine aren't as bad as her's were and she had cramps that made her faint from the age of 9 (even though she didn't start her period until she was 12) to the age of 32.
So you aren't alone and if you need anyone to talk to, I understand the pain.