Can i take cystex and tylenol (acetaminophen) 3 for uti pain?

No problem: Cystex has Aspirin like product and mild antibiotic, which should not interact with tylenol (acetaminophen) #3.

Need to examine: If you need to take two pain medications for UTI, it may be more serious than a run of the mill UTI and you should consult your doctor. What antibiotic are you taking? Drink enough water so that your urine is mostly colorless. It is not feasible to provide a more meaningful opinion without additional history, physical examination and may be some tests.