I believe I have a UTI. What can I take over the counter that will shorten the duration, and ease my side and back pain?

Don't do it! It would be dangerous to continue trying to manage this yourself. You need to see a doctor and, if the diagnosis is confirmed, an antibiotic by prescription. Back and side pain suggest the UTI involves your kidney (pyelonephritis), which will not clear up without antibiotics and could be extremely serious, even fatal. There are no OTC drugs that will help this. See a doctor ASAP!
Cranberry tabs. Best option is to call your clinician. Many offices have protocol to treat UTIs over the phone in young healthy established patients with classic symptoms. Otherwise, can try cranberry tabs (mixed evidence), pyridium (phenazopyridine) of burning/urgency, and plenty of water. See you dr asap if symptoms persist or worsen.