Welcome to the forum. You've come to a very good place for support and information.
I have Daughter almost your age with Crohn's. The first advice I would give you, is get in to see a recommended Gastroenterologist asap.
You will likely need to go through some diagnostics to get a clear picture of what stage the disease is at. Not sure if you've had any of these as of yet, but if not, you will likely have a colonoscopy/endoscopy, small bowel follow through, or MRI.
Try not to worry too much at this point. This disease really varies in it's degree of severity. Many people that have Crohn's, have many years of only mild symptoms that are easily controlled. There is quite a list of medications to treat the disease now. Perhaps you could list the current symptoms you are experiencing?
As far as your monthy cycle goes, I'm a male, and really can't comment on that, other than I haven't heard of Crohn's interfering with that. I'm sure you will get some help with that from the female members and moderators here.
Good luck, keep posting, you'll get alot of help here.