Shaving his head should not have altered his hair growth pattern. His hair will come in regardless, how it is meant to - for him. All babies grow hair at different rates and in stages. One of my kids had sideburns but was bald. You really can't control these things - and to try to even it up (I assume that's why you shaved his head) is not a good idea. Ingrown hairs and stubble .. not to mention their heads are so fragile.
Bald spots are completely normal for babies. Their heads rub on mattress, car seats, baby chairs and swings. Wherever their head presses up against something. Their hair is so fine it just rubs off. You can't prevent this. As their hair comes in and grows thicker, it no longer happens.
Not to sound judgmental but shaving a baby's head ... makes me kind of queasy. When he's got a lot more hair (around 1 1/2 or 2) the most I would do is just gently trim any long loose stray hairs. But no razors or shavers. That just makes me nervous.