It’s probably cysts, caused by sweating or rubbing sometimes
It's quite common for women to have such bumps once in a while, as long as it doesn't stay with you, and it's not painful or jumps from one part of your private to another, then it's nothing to worry about.
As women, we have several phases of hormonal changes, this could be the cause, or like miss Vera said, it could be a transfer of irratation. Try washing your hands thoroughly before masturbation, and using brand new blades or shaving sticks before shaving, it sounds like you have an extra sensitive pubic area. All the best. xx
Herpes would become open and ungodly painfull sores (trust me, i know). They would appear in clusters and burst open, Searing pain, etc. from what you've stated, your lack of sexual contact and description of the bumps, i wouldnt call it herpes.
BUT, tiny pimples from time to time is pretty common. i've had them as well. Sometimes its just tiny irritation from an ingrown hair from shaving, or what have you. Im not really so sure its related to masturbation, but if you think about it, you get pimples because of the oil on your skin. If your constantly touching yourself, there could be some transfer into irritated skin and viola!
Like i said, i get the same thing, or so it sounds like. Its normal as far as i can consider it, maybe talk to a dermatologist or your obgyn if its overly bothersome.
Or try changing bodywash or better skin care after shaving? All i got, sorry!