You should start using SPF 40 for your skin to avoid sunburns.. may be your skin is very sensitive. Don't leave your house without applying SPF, it very important as your skin is sensitive.
Try sunscreens available exclusively at chemists. They are more powerful and for special needs' skin. I use SpectraBan Sensitive 30. It works for me. try it or maybe you can consult a dermatologist and ask her to prescribe one.
There are a few reasons why your skin might get red even after you've used sunscreen. It could be that you're using a sunscreen that's not right for your skin type, or that you're not CBD and Stress applying enough sunscreen. It's also possible that you're spending too much time in the sun. If you're not careful, you could end up with a sunburn.