I would see the dermatologist just to see what he/she says.
If you do have seb. dermatitis, it is often caused by a fungal infection and should not be treated with steroids (because the steroids only suppress the symptoms, they do not treat the cause). Tea tree oil, rosemary oil, etc. may be helpful. You might want to find a shampoo and/or body-wash that has tea tree and rosemary oils in it and see if that helps any (rotate between the tea tree/rosemary shampoo and regular shampoo to increase effectiveness of the tea tree & rosemary oils). Also, food allergies can manifest as a rash that would respond to steroid cream, so you might also want to get tested for food allergies just to make sure.
Also, the item causing the rash may not be obvious. I had a strange intermittant rash on my face for a couple of years - it would break out when I went out in the sun, then go away if I stayed indoors for a couple of weeks. I thought it was due to an autoimmune disease, but it turns out that the hand dishwashing soap I was using to clean my eyeglasses, wash my hands, etc., was leaving a residue on my skin that was interacting with sunlight and causing the rash. I have not had the rash since I changed to a different brand of hand dishwashing soap.
I hope this helps - take care,
Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD (Lupus?), Osteoporosis, Anemia, T- & B-Cell Lymphopenia, malabsorption/malnutrition, Lyme Disease (Igenex Lab IgM WesternBlot positive/CDC negative), etc.
Meds: Pulmicort, Injectable Vitamin B12, Herbs, Nutritional Supplements, Homeopathy.