Suggest Treatment For Weakness,muscle Pain And Lack Of Energy

Hello, I have just got out of the hospital last night. I went to the emergency room for chest pains and fatique that has lasted for about a month . I got a flu shot last month and i have felt bad ever since, I went to my family doctor and he said that i had an upper respiratory infection and gave me the z-pack. I took that and still felt bad , went back and he gave me a steroid shot bacause I was having trouble breathing. That still didn't help much so he gave me some prednisone and i felt better with my breathing after that but I fill terrible. I have no energy at all and my legs feel weak and achy. My muscles hurt. I can,t do any house work or much of anything. I am a white female, 56 yrs. old. They ran a lot of tests while i was in the hospital, x-rays, stress test, blood work, everthing checked out fine but i still do not feel any better. I saw a Rheumatologist also while i was in the hospital. She wants me to start taking Flexiril. Do you have any answers to my problem?