Just a follow-up to the above. It took my scalp 22 days to completely clear up. (I know this is very dependent on the individual and some clear up quicker and others may take a while longer) Now I have a very smooth scalp after I shave with no razor burns, nicks or bumps. Once I saw my scalp was clearing I started shaving every day. Keep with it and don't give up.
For those that say "shave with the grain", I really don't see the point. If I'm shaving my head, I want it slick at least for a few hours.
...Obsessing over a tiny bit of roughness will invariably lead to a cut or at the very least excessive redness. I've learned two things about this... one, what I obsess over nobody can even see and two, in a few hours I'll have a lot of roughness as my hair grows anyway.
...a head that's a little less smooth is better than a smooth head covered with bumps and blemishes.