Scalp Condition

I have no idea what is going on with my scalp!  I'm extremely clean, so I was my hair, condition, just the ends, so it doesn't touch my scalp, yet, after my hair is dried, I can scratch my scalp and I get this white, sometimes beige sort of oily residue underneath my nails.  As the day progresses, it becomes thicker and my scalp gets oilier and by the next day, I have to wash it again because I can't stand how dirty it feels.  By the second day, my hair smells dirty.  Occasionally, I will get pimples on my scalp, as well.  This has progressively gotten worse within the last year or so.  My doctor prescribed a red shampoo and  I've bought things over the internet, used dandruff shampoo, tried baking soda, tea tree oil, nothing works!  I've used shampoo for normal hair, dry hair, oily hair, hypoallergenic, etc.  I've changed shampoos and conditioners so often and nothing helps!  I don't know if it's some type of yeast or what.  I don't have a flakey scalp, so I don't think it's dandruff.  It's simply oily or creamy, whiteish residue all over my scalp with a pimple here and there.  I want to know if there is a name for it and what can I do to cure or treat it.  I'm sick of feeling embarrassed about it.