Baby Diagnosed With Urinary Infection. On Antibiotics. Blood Tests Normal. Serious Internal Problem?

Hi Mr Stephen, My little baby boy was born in Norway on the 5th of dec 2012 is about 2 months old.He was recently diagnosed with urine infection and is on an antibiotic course for 1 week.He had a fever about 38c but the blood tests came normal. He was admitted in the hospital for a day where they started his course of antibiotics and also took and ultrasound in which the doctor could see that the left kidney was slightly larger than the right one.Although she was not sure as the baby was moving alot.They have advised us to get another urine test done for the baby after 2 weeks and have told us to get a scintography done after 6 months from now, just to check if the kidneys were fine. I am very worried with all these developments in my baby.He is having very severe rash in his bumps and poo s every time he is drinking milk due to the effect of antibiotics. My question is according to your experience,is it common for babies in this age to have urine infection and since the blood tests are all normal do you feel that it could be an external infection or any internal problem. Also, if their is any serious problem is it treatable. Thanks for your expert advice. Regards Sona Email- YYYY@YYYY