Very small pimple on my perineum?? not painful at all but it has a white head..

Pimple: could be a pimple or hair follicle infection. You really didn't ask a question here, but acne like lesions and hair follicle infections are very common in this region. IF it appears to be spreading though, don't make the assumption that its a pimple. Spreading pustules can be the appearance of herpes as well.

Probably: a blocked follicle or a blocked sebaceous gland. Use warm compresses. As long as it is not painful and it is only one, most likely noothing to worry about.

Simple pimple: Your description suggests a "pimple", when it is opened, kept dry and clean, it should heal without a problem. If not, see your GYN.