Why do the roots of my hair feel and look greasy straight from the shower?

Listen, people. I am going a little nuts here.

For years, I have purchased two sets of shampoos/conditioners, and switch off every other day, so I never use the same brand two days in a row. This was suggested to me years and years ago by a stylist, after I was despondent about the state of my hair. She said that using the same one over and over and over can cause buildup, and using another brand should wash the buildup away. This has worked perfectly for I couldn’t even tell you how long.

Several months ago, I noticed when I got out of the shower and started to blow dry my hair (a rare occurrence as I usually just throw it up wet and wear it that way all day), it was sort of greasy/waxy at the roots. I figured maybe I didn’t rinse it out all the way… happens sometimes… and just threw it back like I usually would. I sort of forgot about it, because I didn’t try to wear my hair down again for a good long while, but when I started to dry my hair, I noticed the same problem. I thought it a bit too much to be a coincidence, so I made note to not use conditioner the next time, and to make sure I put in the extra time to really thoroughly wash out the shampoo.

Same problem.

So I bought a clarifying shampoo, and used it this morning. I thought briefly that it was working, because when I ran my fingers back through my hair, it appeared to fall back down… whereas before, it would stay back. I went in the bathroom to blow-dry it, and of course, it was still fricking gross looking at the roots.

This is starting to drive me a bit insane. I HATE having greasy hair. HATE. It makes me feel extremely self conscious and dirty. How can I fix this?

I need to point out that I am a month post-op from having gastric bypass, and one of the major side-effects is hair loss. This started well before my surgery. And while I haven’t noticed any loss, I am still firmly within the window of time that this most commonly occurs, so I need suggestions that aren’t too rough on the follicles, just to play it safe.