Could someone tell me why my oranges this year are not as sweet as they were previous years? They kind of taste blan.

Many factors:
harvested too early, especially if your nights are a lot cooler than days, the colors are deep orange but actually still not ready for eating.
not enough K fertilizers and perhaps other nutrients.
slightly cooler temps when the juices are filling up.
over or under watering during the juice filling up period.
and other factors.