How to turn my stringy hair into soft curls?

My hair is naturally curly and lately it wont do anything! Ive tried different shampoo/conditioner, different styling products and nothing helps! :- / Its really stringy and frizzy and looks like i havent washed it in two weeks, and wont curl very good. Idk what the deal is but its makin me so mad! Lol. I use a diffuser and im open to try anything! Thanks!