My heart rate started dropping low right before my period started. I was taking Flagyl and am now taking Augmentin and Clindomyacin for an infection. I am on my period and my resting heart rate is in the 50 s. Sometimes it has dropped into the high 40 s. I had a stress test, echo and 2 event monitors (30 days each, last was december 2011) and blood work and EKG s...all show normal heart function. I was diagnosed with an arrythmia and have had a fib 3 times in the last year at which time I take Flecanide (sp?). Thoughts why my heart rate is low, my neck also feels pressure and sore on the sides. Is it from fighting a possible infection?