Crohn's Disease & Ulcerative Colitis Support Group
Crohn's disease is a systemic inflammatory bowel disease (IBD) of unknown cause, that results in chronic inflammation of the intestinal tract. It can affect the entire gastrointestinal tract from mouth to anus, and can also cause complications outside of the gastrointestinal tract. There is no known medical or surgical cure for Crohn's disease, but there are many medical...

I also don't know that fibro and UC are really connected. I think it is more a thing where it is typical for a person who has one autoimmune disease to have multiple autoimmune diseases.
Personally, Ibuprofen and anything similar causes my UC to get worse, so I avoid it. Probably why your GI is advising that you avoid the Aleve.
I know there are other types of pain medication available for Fibromyalgia. My Mother is diagnosed with fibro and takes something (can't remember the name). It is prescription, but does give her good relief. There are also prescription pain meds for the osteoarthritis that would work with your UC and even help when you have pain from your UC.
You if OTC meds that work with UC do not work for your other issues you will probably have to get prescription meds for the fibro and the osteoarthritis. Unless someone else has other ideas that I am not aware of. I hope someone does! :)
If not - I have found that Ultram works well for many of my arthritis type pains as well as UC pains and does not upset my UC. Norco is stronger and also works with the UC. Makes me sleepy, but better than being in horrible pain. Besides, if I am in horrible pain it doesn't make me sleepy, it just calms the pain (like it is meant to do). Also, Skelaxin works well as a muscle relaxer. I'm sure there are other prescription meds that work well with UC and your other issues. These are just the three pain meds that I have experience with.
I would mostly recommend talking with your GI and GP (or whom ever is managing your fibro and arthritis) about how to manage the three together.
Sorry you now have to deal with the UC as well! What meds are they putting you on for the UC? Some UC meds also help with certain types of arthritis pain.
Please post here when you have questions or just need to vent. I came here when I was first diagnosed with UC and it was a great help to me. There are a lot of helpful people.
Good luck and have a good weekend. :)
Rachel A