My head is gross

Ok, so for awhile now I've only been washing my hair twice a week. I used to do it every other day (don't worry, I shower every day!) and after reading all kinds of articles about how hair and the scalp work I gradually spread out the washings until now it's part of my Sunday night and Thursday night routine. During this process I had Craig keep checking my scalp to make sure nothing funky was going on. He said that at first it looked pretty dry in spots when I was washing it more frequently but now it looks very healthy. Then a few weeks ago we went swimming at his parents' house and afterwards I felt this lump on my head. He looked at it and my mother in law looked at and they decided it was just a cyst. I couldn't stop picking at, wanting to pop it like a zit and have it go away. And now two nights ago I felt a hard crusty lump on the other side and Craig said it looked like another cyst except more advanced and it had exploded nasty gunky stuff in my hair. I managed to pick it all out but now I'm afraid of more showing up. Is this normal? Am I doing something wrong with my hair routine? My hair stylist says my hair looks good as well. Is there a way of helping your scalp stay clean without shampooing or is that the only option?