If you have a history of Psoriasis
then you need to see a dermatologist
so that he can examine you live,as you know Psoriasis is a chronic inflammatory process with relapsing and remitting episodes. So the incident at the swimming pool could be just a coincidence.
so i am sorry but i can not comment any further due to very brief history and already estaiblished case of psoriasis.
i hope you understand that.