It sounds like you were dealing with a bite issue all along. All your symptoms are indicative of a reversible pulpitis. An adjustment to your filling would have alleviated a lot of your distress. It is common for this scenario to happen when back molars are filled because the compression forces are at their strongest toward the back of the mouth. The clindamycin helped the inflammation, but chances are there was never an infection. Your grinding eventually made the necessary adjustments. Please do not extract this tooth, second molars are important!
P.S. X-rays before and after treatment along with a visual exam would be the most accurate way to diagnose your condition.