Diagnosed for epididymo-orchitis 2 weeks ago. i've completed the 5 days cefalexin antibiotic tablets. no pain now but mild swelling. can i masturbate?

No harm: Masturbation probably won't hurt anything. At your age (19) by far the most common causes of epididymitis are chlamydia and gonorrhea, although these aren't possible if not at risk for STDs (new sex partner etc). Cephalexin won't cure chlamydia and is borderline for gonorrhea, but might work on other bacteria that can cause this problem. Re-check with your doctor if any doubt about all this.