My Hair Gets Greasy After 6hrs. I Have Tried All

My hair gets greasy after 6hrs. I have tried all different shampoos for greasy hair and rinsing with diluted bio apple cider vinegar and nothing works. My hair always had to be washed every 2 days but now it's everyday (since about a year). I'm 31 yrs old and in good shape. What could be the cause? And is there something else I could try to get rid of this problem?