Psoriasis or Fungus or ???

My dermatologist said I "might have psoriasis" and left it at that.  I've got pitting in 5 nails, my cuticles are receeding on a couple of those fingers with the pitting, and the fingertips of the affected nails are cracked and dry.  I've also had some discoloration and the nail is peeling away from the bed.  They're getting to be quite painful.  Other than that, I've had no other symptoms.  This first started in my 30s, and I've heard that signs of psoriasis show up much earlier.  My cousin has severe psoriasis with psoriatic (sp) arthritis that appeared in his teens.

This sure LOOKS like nail psoriasis pics I've seen on the internet.  How can I know for sure?  Are there tests?  Are there any preventative measures I can take?  I've been using Cerave, Aquaphor, Cetaphil, neosporin, and even olive oil and am having NO luck with any improvements to the cracked skin.  I know I'm kind of out of luck with the nails. :(  What is the likelihood that this will stay just in my nails?