Greasy hair/ scalp?

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I need advice on how to get rid of this?!😩 Lately when I'm going to do my hair ( especially straighting it) the top of my hair won't corporate! I run my fingers through it and I notice a oily texture. Now I always have my hair in a ponytail or bun because having it down looks so dull😕.

Pleaseeeee any hair advice I'll take it!