Hello,
It can be due to pityriasis rosea. Pityriasis rosea is a common human skin disease which presents as numerous patches of pink or red oval rash. The rash may be accompanied by low-grade headache, fever, nausea and fatigue and itching. Topical and oral steroids are needed. Water, sweat, and soap may cause irritation and should be avoided in the disease. Topical zinc oxide and calamine lotion are useful for pruritus.
Initially, a primary plaque, called a herald patch, is seen. Then it is followed by a distinctive, generalized rash 1-2 weeks later. The rash lasts approximately 2-6 weeks and is found in a Christmas tree pattern over the trunk and abdomen.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It could be a sign of food allergies. Celiac disease has a particular rash called dermatitis herpetiformis. It can affect the scalp too. Crohn's disease can also cause skin eruptions. I would recommend labs be drawn for Celiac disease and a colonoscopy be done for Crohn's, especially if you have any digestive symptoms. If you are cleared of those, try eliminating nuts or dairy from your diet.
Topically you could use a tea tree oil soap and see if that works. Tea tree oil treats bacterial and fungal problems.
Seborrheic dermatitis would be the primary diagnosis ( petaloid seborrheic dermatitis) with 'pityrisais rosea' coming as close second (Unlikely with such a long duration and scalp involvement)
Guess would respond to ketoconazole cremes. Do consult your doc.