I use to have the same problem but now I only wash my hair twice a week, and it doesn't get greasy that quickly anymore, here's what I did:
Week by week slowly decrease the amount of times you wash your hair, (e.g. go from everyday to every other day the next week, then on the 3rd week wash your hair 2/3 times a week. Then stick to washing your hair twice a week, your scalp will start to get use to this and not produce as much oil. Also use a sulfate free shampoo so it's not too harsh on your hair.
I rinse my hair with water to get rid of oils then shampoo my hair twice, after that I use a conditioner and a deep conditioner once a week to keep my hair healthy