Need assistance on my sebbhoriac_dermati

I have been suffering from dandruff as well as sebbhoriac dermatitis (on face, near nose and cheek area) Is it diet sensitive? I've noticed on clean diet it spreads less and do I have to go for a full skincare routine to keep it under control? All the dermatologists I've visited don't help me they just call me thrice a month and only leech money, I know that it has no permanent cure but they don't even tell me how to keep it under control if I want My flare up happens When I eat allopathic medicine (fever or anything) Food dies,  sucralose etc and artifical flavours too, Do fried food and spices play major role? Does gluten play role? I am helpless and need assistance please help. As much as I know it causes by yeast overgrowth, what causes the growth? How can I know the root cause of it I don't wanna be on meditation all my life, What skincare should I do to minimize flaring without using steroids or harsh creams, Due to seb derm my skin has aged a lot and at age 17 I look like 22