Male 50 y.o. intermittent stinging urination while sitting (forward sitting), standing is ok no stinging sensation. too much masturbation?

Stinging urination: I think you're probably describing prostatitis, a condition your doctor can diagnose right in the clinic for you. Too much masturbation? I think you'd be pretty hard pressed to find any scientific data on that one!

Antibiotics: You should get a urinalysis and urine culture, as well as prostate secretion cultures, especially with burning sensation on urination, because you may have a urinary tract or prostatic infection. You can do that at your primary care physician. They will prescribe you appropriate antibiotics.