My Left Upper Arm Muscle Is Sore And Aches And

My left upper arm muscle is sore and aches and the area feels warm. I had my joints checked out with a doctor and there is no problem with movement. This muscle has been sore for several weeks and I thought it was stress but I am not in any pressure situation and I do take Flexeril and Ibuprofen daily. I have not be in any accidents. My right upper arm muscle was sore but it has cleared up.