Fouettes on pointe help?

So I've been on pointe for three years and I still can't do fouettes on pointe. I really want to be able to this year because my teacher said she's putting them in our dance in the spring and I really want her to pick me to do them. So I figured I would start practicing now. My fouettes on flat are really good (to the right anyway haha) and I can do good singles and okay double piroeuttes on pointe. I'm not sure if I just don't have enough strength or what, but I really can't do fouettes on pointe... I'm not scared or anything either. Please help!! I need to have these by February at the latest. And yes, I know it takes time and practice and all of that.