I've masturbated 7 times yesterday and my testicles started to hurt today..what is the reason?

Discomfort is a signal from your body that you exceeded its reserve. If you don't overdo such things the body can handle it without such signals. Take it easy for a while. It will self heal.

Agree with Dr. Ferguson. Excessive sexual stimulation caused vascular congestion of the groin, including testes and that is the basis of the pain. Give it a rest. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.