Hello,
From the symptoms the possibility of seborrheic dermatitis is unlikely. It can be due to boils or irritated hair follicles. In case of boil inside the nose which is infection of the hair follicle inside the nose, it takes its own course for a week or so in healing and no treatment may be required. Apply warm moist compresses three or four times a day over the tender area. This will help to bring the boil to a head and encourage easy drainage.
Along with the warm compresses, you can take OTC pain killers and a course of antibiotics if the causative agent is bacteria. If the symptoms persist then get an examination done from a dermatologist.
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 regards.
To give you an idea of what my seborrheic dermatitis looks like see my post:
http://www.medhelp.org/posts/Dermatology/Stubborn-Skin-condition/show/1258944