Excellent points, Cindee. High doses of any NSAID are always prescribed with something to protect your stomach. It is important to have doctor supervison of any long term medications.
Just a warning about the Advil--you can take it, but be careful of using really high doses. I was prescribed very high dose ibuprophen for about a year, and I got stomach ulcers from it. Maybe switch off with Tylenol sometimes if the pain is mild, of course, too much Tylenol is not good either.
I would not lift heavy weights--maybe do lighter weights with more reps. The yoga is good. Running--it's hard on the knees and back I think. Maybe you can cross-train and do some bike and elliptical.
AS, like any condition, is best diagnosed and treated early. If you think you have AS, I strongly suggest you get some kind of health insurance as, after diagnosis, you will have a tough time getting insurance other than through a group policy.
If ibuprofen provides relief, that is a good indication that you may be dealing with a mild case or something completely different.
Stay as physically active as you can. Since you are in pain, you should probably get with a therapist or trainer to determine what exercises are going to be beneficial to you and not harm any conditions you have, AS or otherwise.