I'm on accutane so why is the crown of my head greasy?

My hair has always been a little bit on the greasy side but it was never noticable until about the second or third day after washing my hair. Currently I am on a form of accutane called claravis (this is my fourth month) and my hair can hold up to three days without being washed and it still looks clean. Still I am used to having slightly oily hair so I still wash my hair everyday. But all the sudden yesterday I noticed, after my hair air dried, that I had a greasy spot on the crown of my head and nowhere else. Its kind of waxy feeling and almost seems like I didn't wash out my conditioner but the thing is I never use conditioner on my roots. I made sure I got all the residue out of my hair today but the greasy spot is still there. I'm so confused because accutane poisons your oil glands and significantly reduces their production. Also I started sleeping on a towel the past few nights so my moisturizer wouldn't get in my hair. Could that be it? But I keep my hair up in a bun. And I haven't changed any of my hair products. What could this be?? Someone please help me and my very sad hair :[