I've had trimethoprim for a uti which made me feel sick then I was put on a 3 day course of neurfuntin. ( I think) Then my go put me on ciprofloxacin but reading the info it says that theses tablets can cause tendon and joint pain( I had a ruptured Achilles' tendon a few years. Ago and did not want to risk it ). I am now on my second day of 500 mg of amoxicillin ( three times daily) and still have the constant urge to pass urine. How long do they normally take to work.