I have a rash on my elbows and knees and it was sudden. Never had skin issues in the past and II am 34. Could you suggest what it may be?

Rash. Rashes in the areas you mentioned could be many - but psoriasis comes up first? Have this checked out.
Maybe, but first... With the small amount of information you've provided, the possibilities are too numerous to list. The only way physicians laser into this question and provide realistic answers is for you to be as specific as possible with time lines, product exposure, allergic history, medications taken, etc: atopic dermatitis (eczema) and psoriasis come to mind in the anatomic areas you describe. See an md!