It's either burning it or leaking it, there are no other options.

How many miles do you drive in a month? 

Same thing with my 3.7lt 2010 Toyota Yaris, it gets around 2lt or less after 4000~5000km.

As some people may say, even if you don't see white fumes, or smell, it might be burning in small quantities, if not that, it may be leaking. Check the bottom and top around the gaskets or seals.

I had my head gasket and other parts inspected already and the only recomendations i've got from there were to either replace the rings and caps (<_<) or decarbonizing. Since the motor was still running ok, and the oil wasn't that bad (still had a decent color and considerable viscosity), just low, i considered toping of to half until it reached 5000km or 5500km but i ended up replacing the old oil and filter (5800km) because i didn't have any spare oil resting in my house and i didn't want to use the car with the oil on low even thought the motor wasn't making noises and didn't get a oil pressure light. The secret is to not trust blindly on the pedometer, and regularly check the stick, just like you do with the coolants, old cars can be tricky sometimes.