Hi C, These could be Petechiae, there just small bruises of a pinpoint size, or small red spots, these should just go, I think your find this problem of yours has come form your grip, its to tight, we you masturbate, this should be the same as having sex, and when you get round to that, your find its just a featherlight touch.
From now on just masturbate with a featherlight touch, it make take some time, reason for this, you need to re-educate your brain, to this new style of masturbating.
Good Luck
It is normal trauma from friction. You need to use more lube or better lube. Lotion works. To treat it, try clear 100% aloe vera.