ACNE ON MY SCALP

So I had this problem when I was like 13 
Well I'm 21 and I apparently have this problem again 🙄 
I have acne on my scalp under my hair.  One popped up and before you know it, atleast 4 Huge, painful pimples. Funny thing is, it's the only place I have them. I scrub my head and wash my hair like I'm supposed to, but you can't really put acne wash on your hair because hello frizz. I'm wondering if it's my shampoo, idk. I'm just looking for some kind of advice.