Cramps in abdomen and diarrhea followed by swelling of ringfinger tip with blisters filled with liquid, itchy, painful, red and tender to touch. what could the causes be?

Celiac Enteropathy.: It sounds classically like what patients with celiac or gluten enteropathy experience. The swelling and blistering of your fingertip may be a dermatological condition in the syndrome known as dermatitis herpetiformis (no relation to any of the herpes viruses as the name may connote). The gold standard for diagnosis is getting an anti-transglutaminase antibody blood test checked with your doctor.

Shingles, maybe.: The diarrhea & cramps may have many causes, including a stomach virus. The blisters on 1 finger may be due to shingles (Herpes zoster), a viral infection & may be precipitated by stress (as w/acute illness). Don't scratch the blisters, or it will scar. Please see your doc to confirm your diagnosis & to see if treatment is indicated for either problem. The drug for zoster works best taken early

Multiple symptoms : Painful finger may be infection that requires medication so please get examined. Not sure if all your symptoms are related