I shaved my head, now I've developed a farm of white-pus filled bumps, there is a bump on the right back side of my head. What can this bump be?

Razor bumps? Pseudofolliculitis barbae is a fancy word for razor bumps. More so in dark-skinned people, shaving closely with a razor can cause new very short hairs to grow down in to the skin, causing irritation. It's also possible to have an acne-type response to shaving, and it's possible to introduce infection as well. Warm compresses can be helpful, gentle cleansing with hypoallergenic soap.