My hair only gets oily at the top.
And it's flat, so I use a volumizing shampoo and conditioner, called Amplify, I think.
I have thick hair, and I also already have layers.
I blow dry it Mon- Fri night after I take a shower and before I go to sleep, because it helps with the volume.
But on weekends when I don't blow dry it, it gets flat and oily.
I also straighten my hair Mon-Fri morning, but that never caused any problems cause I use a heat protectant.
How do I stop oily hair when I don't use a blowdryer?

*I don't plan to switch shampoos or conditioners for a while because the shampoo and conditioner I have came in a big bottle.
* No hairspray or mousse suggestions too.