I've had what sounds similar to this sort of pain off and on for all of my adult life. I don't remember any doctor saying it was an infection. They have suggested muscle tension and a need to relax. I've had bursitis and another form of joint inflammation that I can't remember the name of now. Always they call it an inflammation and the pain has usually gone away within a few weeks. The recommend and I use ibuprofen for the pain.
When the pain doesn't go away they give me a 10 day treatment of a steroid and it's always gone away then. They say they don't actually know what is causing the pain.
During one of my last bouts of this sort of pain the doctor sent me to a neurologist who ran tests on the nerves in my hand and arm. this time that was the only location of my pain. He said I had minor nerve damage and maybe the beginning of carpal tunnel and proscribed neurontin, saying it was off label. That was years ago. The pain went away.
My brother is having a lot of muscle pain in his neck, shoulder, and arm. Right side. Because he's had back surgery they've been assuming it was related to his back. Recently they decided he'd torn a muscle in his shoulder when his bicep became noticeably swollen and hard to the touch.
They think this is a secondary injury related to the back stuff.
Anyway, the point of this is that his doctor prescribed gabepentin which does noticeably reduce his pain. I learned that it is the same thing as neurontin. It is a pain medication with a design to work specifically on muscles or nerves. I don't remember which.
If the pain doesn't go away you could ask about the neurontin.
Much of my pain was caused by carrying heavy objects with my hand held down at my side. Since I stopped carrying a 30 lb bag of leg irons I don't have as much pain. LOL Another cause of my pain has been repetitive motions such as opening a closing a car door dozens of time each day. You might evaluate your daily movements and see if certain movements make the pain worse.