If 23 year old male got 20 viral infections in 1 year.cold,gastroenteritis,sinusitis. all resolve without treatment, is it concern though ?

Immunodeficiency : On average, a person can get 5 or 6 colds and coughs per year. You're reporting 3 times that amount, so I suspect something is wrong. Chronic stress will weaken the immune system as will lack of sleep--but I think u need a formal evaluation to make sure there's nothing else seriously wrong. Obviously paying attention to hygiene should help- try hand washing frequently, avoid handshakes etc.