Dextromethorphan

I am a 41 year old white female After taking OTC delsym for a cough I developed pain in my back left side and severe fatigue, no energy. Thinking at first the illness just "zapped" me. I continued the medication for the cough. I was not able to get off the couch because of the fatigue and the pain just got worse in my back and moved to the upper left abdominal quadrant. I also developed a pounding headache. I was starting to get very nervous that something was REALLY wrong with me, but not thinking it was the cough syrup, my cough got better but the pain persisted, I stopped taking the cough syrup as often (no more that directed on the bottle) the next day felt a LITTLE (still had discomfort in back and abdominal not pain) better then had a coughing fit around 3:00 pm took more syrup and within an hour the pain started to return by that evening unable to get off the couch again and pain returned full force. Not sure why I had such a problem this time as I have taken this in the past without these side effects.