Thoracic Nerve Pain Gone When Taking Amoxicillin

I have been suffering from thoracic pain for several years. Occasionally the pain gets so bad that I receive trigger point injections. There is something going on with nerves, which causes the pain to shoot around my right side rib cage.
Now I have realised that when taking 500 mg of amoxicillin three times a day for upper respiratory ailments the pain in my thoracic back vanishes. After a week of stopping the dosage the pain returns. Sometime with a vengence.
This has happened three times. Anybody experience anything this? Any possible reasons?