Burning Oil

I just changed out my 5W-30 oil today to 20W-50. After emptying out the old oil into a milk jug, it only filled about half the jug. That's only 2 quarts left over after the oil change! I haven't seen any sign of leakage, so would that mean I'm burning the other 2.5 quarts? Possibly do a compression test?

Compression test, watch your exhaust for blue smoke, and get under the car and look for leaks. Some are easy to overlook.