I have psoriasis so I've been laying out in the sun and I've got a rash that itches? What could this be and what can I do to prevent it for happing?

Itchy sun rash. Sun exposure rashes could mean a reaction to your sunscreen or a "sun allergy" like polymorphous light reaction (pmle). 90% of sun rashes are due to pmle, but there are other conditions that can make you sensitive to sunlight. If the rash is from the sun, the areas that were exposed to the sun would be most affected. Also, sunburn would make your psoriasis itch. This needs evaluation.