What Causes Bumps On Mastoid And Itchy Scalp?

I have a series of bumps on my mastoid bone behind both ears. I also have a bump on my neck. Started out with 1 bump on one ear on Tuesday and now there are 6 in total. My scalp also started being super itchy on Sunday. Not sure if the itchy scalp is related in any way. I have no fever and feel fine. What is causing the bumps?