My skin will burn no matter how much sunscreen I put on. What works?

I go out in the sun every now and again but nowadays my skin is burning like nobody's business. I need help to make it stop burning and being so sensitive. I always wear a hat and sunscreen (bullfrog spf 36). Yet it still seems like I have to get burned. Please help find a way to make my skin more resistant to the sun, or at least find a sunscreen that works.