What Causes Itchy Rashes On The Body Along With Headaches?

I am 25 years old and for about two and a half months i have been suffering a horrible rash. it first started out in the back of my neck and then spread to my back, my arms, behind my ears, and my hips. i was treated for contact dermatitis with prednisone on a 7 day cycle and it almost went away. a week later i was back ten times worse. then the doc said it was scabies. then not and now she says its either eczema or psoriasis. i have headaches, very irregular periods, all of my lymph nodes in my neck are swollen, i still have rash on my neck, chest and in my hair..... very itchy..... nothing relives it but halogal and prednisone.