Two bumps in the back of my 17 month olds head

Hi everyone! I have noticed recently my son has two bumps in the back of his head one on each side of the back. Every time I touch them he doesn’t seem too comfortable and often scratches his head near the area. They seem like lumps not pimple size bumps. I’m not sure if it’s normal for children at his age to have them. He hit his head a few weeks ago but didn’t have any symptoms that normally come when a child has hit his head like, vomiting, fatigue, etc.