Array of skin disorders, what's the common nucleus?

I have an array of skin disorders.  I have dandruff, athlete's foot, dry hair, dry skin, dry lips, backne, oily/congested pores.  I feel like anything that involves the skin or hair is of extremely poor quality.  Even just splashing my face with water or pouring some water over my head will dry me out.

I drink a lot of water everyday; it's pretty much all I drink.  I don't use hot water; I use tepid water.  I exercise.  I eat well.  Honestly, I have pretty high standards and I think I live really well.  Yet I still have these issues.

I know there are separate treatments for each individual condition.  I am treating each condition differently, and it helps.  But none of the issues ever seem to fully subside.  

It can't be a coincidence that I have all of these skin problems.  There has to be some problem at the root of it.  I haven't been to a doctor that has been able to help me.