If you forgot to pack sunblock, there is nothing to worry about. It’s readily available here in Qatar. But perhaps a little more pricey than back home.
Available in nearly all pharmacies and large supermarkets, a decent sunblock will cost around QAR 57 (GBP 11, USD 15, EUR 13, 818 Peso). And please, please, please make sure you put it on. Or your vacation may be a painful one.