Like everyone is saying, you should go back to the doctor. You won't be wasting their time; it's their job and they're paid for it, and you have a genuine concern. It could just be that the infection hasn't fully gone away, in which case they'll probably put you on another course of antibiotics until it clears. (I had to take antibiotics for almost a month with a chest infection... remembering to take them sucks, but it's nice to be well in the end).
Whilst waiting, have you tried using a hot-water bottle to try ease the pain a little? My mother gets kidney infections quite often, and it's how she eases the symptoms. I'd maybe avoid taking painkillers as well as they might aggravate it a little.