I have been given phenoxymethylpenicillin potassium 500mg 4 times a day by my doctor for sinus congestion and ear pain. today i have sore joints and aching muscles. have taken 5 doses since yesterday.is this meds related or viral? no temperature?

Joint pain is listed as a less common side effect of Peni V. Sinus infection and ear pain are usually caused by viral infection so Peni V likely does not change the outcome unless you have superimposed bacterial infection which I doubt. By benefit vs. risk, I will advise stopping Peni V and observe all symptoms. If joint and muscle pain gets better after 24 - 48 hours, Peni V is the culprit.