sand? i wiped out last week due to some sand that got blown into a corner i normally take at speed, lost traction on the rear wheel.

you are probably somehow having bad luck or you take too much risk when cornering for your skill level. cornering is an art of sorts and not every is good at it, you need to ride within your limits. also think of this once you fell the first time were you more scared when cornering and such, i have a feeling your confidence and mental approach to cornering / riding might have suffered from a few crashes stringed close together.

Don't get down on yourself due to a few crashes, it happens to the best of us. just get on the bike and try to conciously practice your cornering and spotting hazards.