I've been having minor pain in mid back on left
Hello dear, welcome to Ask a doctor service.
I read your query and here is my advice.
According to the symptoms you refer most probably it is costochondritis, an inflammation of the junctions where the upper ribs join with the cartilage that holds them to the breastbone, or sternum. If you press the point with your fingers you may feel pain by compression and this can confirm it.
Costochondritis is a relatively harmless condition and usually goes away without treatment. The cause is usually unknown, but may happen from increased activity involving the arms that's why you refer to have more pain during physical activity.
This is the most probable condition causing your symptoms anyway the MRI will differentiate the condition.
Hope I have answered the question.
Let me know if I can assist you further.