I Am Using Ketaconazole Shampoo For Supposedly Having Seborrheic Dermatitis

I am using ketaconazole shampoo for supposedly having seborrheic dermatitis on my scalp . I have never had itching or any irritation I just noticed that when I would wash my hair and I would run my finger nails through my scalp I would get a white residue under my nails . I was prescribed shampoo and was told to alternate with Selsun blue .... are used to only wash my hair once a week since I was told that was healthier and now only after one day after washing my hair my scalp starts smelling and it seems to be becoming dependent on me washing it every other day which is not easy to do because I have a lot curlier hair with in the past three years than before . Should I go for a second opinion and is it normal for my schedule to get a word smell them before a lot sooner after having wash my hair . Thank you