Seborrheic Dermatitis. This the reason?

I feel like I have started facing this issue when I shifted to Indirapuram from Delhi few years back. I have done my own research, found out that there is a yeast on everyone's scalp but overgrowth of that could lead to this. I have oily scalp, greasy dandruff, waxy white flakes, acne on face too. I have been using ketoconazole shampoo for a while now but it doesn't help completely. I can see reduction, but not eradication. Whenever I comb, I see white buildup falling of. I take bath twice a day, and don't apply oil but still I can't find out the root cause behind this problem of mine. I sometimes feel it's psoriasis but I think it's not, because I have sticky dandruff. I am really concerned because dandruff can make hair shafts smaller and I can see hair falling whenever I shampoo with such chemical based products. Also, the water is very hard in my locality so is this the reason? I don't really now.