Your GP may send you to a Dermatologist or Podiatrist….but you might want to have them take a look. It’s pretty common with Psoriasis and so at very least use some antifungal solution.
You don’t want to lose your toenail or get an infection….

I would see a dermatologist. Could be psoriasis of the nail or some other kind of infection. But if you have psoriasis the Derm should be your primary for that unless you also have psoriatic arthritis/ then the rheumatologist is your primary with Derm as secondary.