My face doesn't get burn that easily and I usually just wouldn't put on sunblock but now looking at it, I realize that I should. So my question is how often do you think I should reapply it.?

YOU SHOULD REPEAT SUNSCREEN EVERY 4 HOURS .

In general, it's recommended to reapply sunscreen every 4 hours if you use it normally. If you are swimming, you need to reapply more often. So it depends on the circumstances.