How do you know the difference between winter dry skin and psoriasis? PLEASE PLEASE PLEASE HELP?

i have a patch on my leg that is dry and itchy. it is not red at all and there are no flakes. i can barely feel it when i touch it or rub my hand over it. it has been there since about...january 5th maybe. it has not grown or anything. i put lotion on it and it goes away a little bit, but not completely. it all started when the weather began getting colder here in january, and being from louisiana, i am not used to this weather. i would takes a picture of my thigh but you can't see the dry skin whatsoever. how do i know if this is winter dry skin or psoriasis? please help! i'm worrying myself sick