Hello,
Thanks for using Healthcaremagic.
I have gone through your query and I can understand your concerns.
Probable diagnosis.     : Seborrheic dermatitis
Investigations needed : Skin scrapings under microscope. RBS(Random Blood Sugar)
Plan of treatment         : Topical and oral antifungals
Outcome                        :Moderate to good.
As per your description it seems that  you are suffering from a skin condition called seborrheic dermatitis.Its a kind of 
fungal infection affecting "seborrheic areas like 
scalp,buttock fold,infra mammary area .
But before commencing the treatment we have to rule out some other skin diseases.I suggest you to 
consult a dermatologist to make a correct diagnosis.A good dermatologist can make a spot diagnosis with a hand 
lens, you might also need a microscope examination of your skin scrapings to confirm the diagnos. Check your blood sugar level to rule out 
diabetes.
Treatment include oral and topical antifungals .Use 
ketoconazole containing shampoo if you have lesion on scalp.You can also take antihistamines like cetrezine to reduce itching.
In unresposive cases you can opt for 
phototherapy but it is relatively more expensive.
Hope this information helps.
Regards.
Dr.Shinas Hussain