How can i grow my hair out faster?

Okay so i have very healthy hair never have i colored it or anything like that. My hair used to grow like 2 and a half inches each month when i was younger. but it seems to be stumped. At the start of the school year my hair was a little below my neck and now it is in the middle of the chest area. I use Morrocan oil, and Sebastian potion 9. FOr shampoo and stuff, i switch each wash with Herbal esence the curl one, and the hydrating one. and morrocan shampoo and conditionar. Every so often i do a hair mask. I dont wash my hair every day, and i have little split ends. SO do you have any tips that could help me? Like should i take any vitamins or something? Also, my hair doesnt get oily like after 2 days. mostly after the third... THANK yoU!