What Causes Lumps Along The Veins Of Biceps?

I have strange bumps lining up directly, not around but perfectly aligned with the veins on my biceps for both arms.. Have never had them before nor seen anyone I workout with has them, im in decent shape and am 15 years old, when working out they pop out very visibly and noticeably and there s about 4 on my right arm and 2 to my left.. No recent health issues or allergies, no change in my workout routines besides maybe increases in the weights I use? At first (about 2 weeks ago) it was only one, but since then more and more have been appearing and im afraid of it being something bad. Does NOT cause pain, but I ve been reluctant to touch them just in case, but they re just kinda soft and Im near certain it s part of the actual vein itself. Thank you for the help! - Dylan