Shaved my head and now it doesn’t grow back

Hello I am a 24 year old American male and I shaved my head not too long ago recently. I have noticed that the hair on top of my head is not growing back as fast or as strong as the hair on the sides of my head even though my hairline is okay I seem to have thinner hair than before. What could be the cause of this? I’ve been taking zinc and a multivitamin for a few weeks now but I haven’t noticed a huge difference yet. And I’m thinking about starting finasteride and minoxidil thanks in advance.

You probably shaved off miniaturized hairs that were not growing and these didn’t come back, just an educated guess