i got this when i first added seperate triceps excercises to my routine, hurts whee the tri joints the bone right?
go easy, use pain as your guide, any movement that hurts, drop for 2 weeks, then you could maybe start back into them LIGHT, slow and steady wins the race, with no injuries!
PS - ExtraMile - wish i started as young as you man, you have a huge advantage and for 15 your lookin built very damn well