Effects Of Taking Ibuprofen?

I have been seeing a pain management specialist for a little more than 3 years. My treatment is OxyContin 20mg every 8 hours , Percocet 10mg every 12 hours ( for break through pain) & tizanidine every 8-12 hours for non retractable chronic neck & back pain. I also take keppra, fioricet + codeine 50/325/40/30w. DHE injections & Botox therapy for chronic migraines. I have always passed my urine test. I was unable to urinate at my last doctor visit & was given a saliva test instead. I failed this test. My doctor has dismissed me as a patient but will not tell me why I failed. I take ibuprofen daily. I have read that ibuprofen can cause a false positive in saliva tests. Is this true & what are my options? Thank you.