I have had this problem too and have been doing some research online. As for the ingrown hairs it's most comon for people with curly hair which I have, I am not sure how to prevent them. But the bumps come from shaving. When you shave the oil that's on your skin naturaly gets into the pores. It helps to exfoliate before you shave. Also applying a product that gets oil out of the skin works. Hope that helps a bit.
-dani