Cherry Trees Dropping Flowers and Not Fruiting

After 5 years my cherry trees still do not fruit. They bud and flower lots filling both trees each year but seem to drop the flowers and not fruit at all, the best giving me 3 or 4 cherries. I have 2 trees one being a 2 way giving me 3 types of cherries. What do I need to do to fix the problem so they can fruit.

Regards,
John