Abdominal pain every month but no bleeding?

hey hey,

I'm 15, and for some time now, I've been having moderate to severe abdominal pain at the same time every month, but I haven't had any bleeding. I've never had that before, just the pain. About a year ago, I had a brownish pre-menstrual bleeding, I'd say, but it was rather greasy.
does anyone know what all this means?

The facts again:

• I haven't had a proper period yet
• I had spotting a year ago
• I have been experiencing severe to moderate abdominal pain at regular intervals for a few months

HELPEEEE