I’m a victim of extreme waswas that makes me spend hours at the bathroom cleaning myself to the point that my skin is so dry that it bleeds. If I don’t spend that long in the bathroom I keep thinking that I’m najis. Should I ignore my doubt even if I’m certain?

OCD is probably what you have. You must get treatment for it. You must ignore the whispers. It’s Shaitan getting to you. Certainty is not same as doubt. But you might have condition which makes you feel it’s certain but in reality it’s not. It’s very important you seek medical help