Is clogged. This is unusual for a field that is only a few years old, but you say you bought the house about 4 years ago. Do you know how old the field is?
When is the last time you had the septic tank pumped? It should be done every 2 years, maximum 3. Otherwise, solids from the tank can build up, flow out into the field and plug it. It sounds like you may have to replace the field, there is no majic repair for a plugged field.
If your drainfield is registered with the local inspectors, then there should be an alternate site for the field location specified.