What Could Throbbing Pain In Chest And Neck Indicate?

Doctor,I'm an eighteen year-old male, and for the past year or so I have had throbbing at random intervals all over my body. Sometimes it lasts for seconds. Others for around half a minute. This has never bothered me until lately when I have had throbbing in my chest and around my neck area.I've been to see my GP who tried to put me at ease. But, I am still worried.What could it be?