Doubtful its a head gasket, or when you pop the hood you would see oil all over the block.

Since you haven't pinpointed any obvious leaks, I'm going to assume your are burning oil.

First, I'd see if the car logged any codes. Head over to an autozone or equivalent store. Most do free OBD2 scans for cars, and would be able to tell you if your ECU logged anything.

Then you get to run through a list, preferably while the vehicle is running since that's when there will be oil pressure. You will need ramps or a pit to do this, so start scouting craigslist for cheap ramps.
Check the Oil filter, make sure its secured properly and sealed.
Check the oil pan, feel the gasket. It might not be an obvious leak if its only leaking off the oil pan. Feel the gasket around the entire pan and make sure its sealed. If you park on hills, the oil might only be leaking out when the car is at an inclination. Odd but it happens.

If not, remove the spark plugs, see if there is oil leaking into the combustion chambers. If its an internal leak, your options are limited. You might as well start calling around junk yards and asking for an engine, since that will be cheaper than having yours repaired. The AAA shop back home does a plug and play swap for only $200 hundred bucks on most domestics. Just source the engine.

Good luck, obviously if you can get a mechanic to diagnose it, you will have the problem solved.