Is it healthy to masturbate three times in a row? like continuously?

Define "healthy". Your body will likely tolerate most of what you do to a point when it makes you sore & stop. Over time it would recover if you moderated the activity. The downside is there are alternative ways to spend time that are more productive in the long run in acquiring a partner to share sex with.

Healthy can be a flexible concept. masturbation is a sexual act and if you want to do it the way you state it is not unhealthy. Just unusual. Moderation in everything is also considered healthy. Try it.

No. Any thing in excess is not healthy. The very fact that you are asking this question suggests that you know that what you are doing is not healthy. 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. Get HPV vaccine. Wish you good health!