I am finding my upper body incredibly stiff. I have been exercising a lot lately, mainly my upper body as well where I'm finding it to be stiff. Could this be strain from exercise? What should I do?
Yes. It might be due to heavy exercise. Also I am worried about rhabdomyolysis which is muscle breakdown and can cause kidney failure. You need to see a doctor and have blood work and urine work done
This certainly may be related to exercise, but I still would make an appointment with your primary care physician for an evaluation.