Hello~How are you feeling now? If not better, then I would add a good, high potency Probiotic to replace the friendly bacteria that he antibiotics have removed.
As to the back pain, this may be due to misaligned vertebrae in your back and also not drinking a lot of water. When on antibiotics, one must always drink extra amounts to counter-react any negative side effects of the drugs. The chiropractor will take some x-rays of your back, after looking over them, he/she will be able to tell what areas need attention; after a few treatments, you should start to feel better.
Hope you are feeling better or will feel better soon. God bless you.