My right testis is bigger than the left one and it also pains, why?

Worth getting seen. You may have a hydrocele, or less likely a tumor. Have your physician check you out. It may be ultrasound time. I also noticed your list of health concerns. Enjoying your body when you're alone isn't a problem -- it's healthy. You may want to talk to a sensible older man -- maybe even dad -- about your newly-grown-up body. Best wishes.