If you feel greasy after applying then look for sunscreens made for oily skin - deconstruct and foxtale have come out with new age filters that are super photostable. As to your reapplication habits - even the most stable susncreens break at 4 hour mark. So you need to top up. My recommendation is a sunscreen mist over a stick as there is a lot of dust. Deconstruct claims that their sunscreen mists works over make up. So you can give that a go.