Hair probs

My whole life I've used tres semme shampoo and conditioner, and sometimes my hair will get into a greasy stage so I use suave once and it'll be alright, I can go back to tres semme. But for some reason it's to a stage that absolutely NOTHING will make it non greasy. I've switched shampoos and conditioner 3 or 4 times, I've tried hair treatment. Nothing will help and I'm getting tired of going around with greasy hair, please help me! What is causing this and how do I fix it??