HELP my doctor says i have seborrheic dermatitis? BUT read more please?

But when i went to the doctor she barely looked at my scalp. I have some dry flakes on my scalp and hair and its worse at night. I have it under control as long as i use this organic shampoo a few times a week. I went to see her to just make sure its nothing bad and see what i have but what she says i have i really dont think i have. Im looking at pics and i dont think i have that. i have no scaling or red patches along my hair line and those are symptoms. She did prescribe me some shampoo for psoriasis which isnt the same as seborrheic dermatitis and i dont think i should use it. im a white teenager and seborrheic dermatitis occurs in males over 50. SO my question is, should i use this medicine? or keep with what ive been doing even though i get flakes from time to time? what do you guys think? i honestly feel my dermatologist was wrong and i just have this torn feeling of whether i should use it or not. Also the shampoo causes hair loss and adrenal glad issues :/ i dont want to make it worse. another thing that causes this is stress and i am stressed so i think i should treat it with my organic shampoo and cut down on the stress. what do u think?