What Causes Bald Spots In Hair?

Hey I recently saw a doctor to see if I could get to the bottom of this problem I've been having with infected hair follicles... I have had a polynomial cyst removed around the tailbone region but a new problem has arrived. Recently I've been getting huge bumps on my head and some I didn't bother to drain because I figured they would go down with a lil anti biotic ointment... however with that said.. there's two spots on my head that have gotten huge and actually left bald spots in my hair. I was hoping you could tell me more about what i can do or what this is exactly. My doc said it was sebaceous cyst but he's never seen a case where it destroyed hair follicles. Please give me a second opinion on this.