Pain in left lower back. Antibiotics?

Hi, I'm experiencing episodes excruciating pain in lower back portion. Each episode lasts for about 2-3 hours, wherein there is severe pain in left lower back followed which sometimes extends till stomach lining in the front. Two of these episodes were while I was sleeping and I had to wake up because of the pain. During these episodes, I feel the tendency to pee very frequently, almost every 10 mins but I'm only able to urinate in small quantities. After the pain goes, everything becomes normal. Prior to this, I was suffering from acute tonsillitis and was on heavy dose of antibiotics (amoxicillin for 5 days, Faropenem for 10 days) which i stopped about a week ago. Does the pain have anything to do with side effects of these antibiotics? Please suggest the way forward.