Painful muscular type pain in my mid back for 3 days. hurts to the touch and very painful to sneeze. active but no new exercise. likely muscle strain?

Probably: Given your age, about 70% of all cases of acute back pain are self limited and due to "myofascial" irritation/strain. Sometimes sneezing can aggravate pain if there is a small tear of the outer coating of the disc capsule but even so there is an excellent chance of total resolution. Stay active, lift using your legs ( don't bend your back forward) and consider ice packs/OTC NSAID for 3-7 days.

Yes : Most likely yes ! You can try warm compresses , light exercise & maybe Flexeril (cyclobenzaprine hcl) (muscle relaxants) prescribed by your doctor ...