Three days after my FUE hair transplant, my scalp and forehead has really gone oily. Why is this?

If your scalp is oily after surgery and you are concerned it is best to contact your doctor. Otherwise there is no way to tell.  Perhaps you have oily scalp and you are not washing well.

This is probably because you have been only gently washing your head for the past few days, allowing oil to build up. Nothing inherently wrong with this, just make sure it doesn't get too out of hand and that you are washing sufficiently to keep your grafts clean and are softening+removing the scabs over time. If your scalp is naturally oily this is okay, if your scalp isn't it may be a sign of insufficient washing.

This is not an issue , no need to worry . In my practice I recommend my patients with an oily skin to wash their hairs twice a day . As mentioned before , by  a good washing the oil will be removed . All the best 

Oily skin on the scalp is not a problem for hair transplant growth. Good washing is critically important and this will remove most of the oils