Not feeling too great about it.
I've been getting a code on and off for a bit, P0139, but it goes away after it cycles, very short lived. I'm about to change my oil and filter tomorrow, making sure my O2 sensors are seated properly to hopefully just rule that out.
I just added some more coolant to my reservoir as well and I can't help but thinking that I'm smelling something sweet. Maybe it's because I'm wanting to smell for it, but I really do think it's out of place. Once my car cools back down in a bit (It's been about 9 hours since I adjusted my coolant level) I'll check and see if there's any difference in my reservoir.
I'm really hoping that I'm just crazy, but my better judgment tells me I have a leak somewhere. This could suck.

 

Check the oil on the dipstick for any sludge from water/oil mixing, and check the coolant reservoir for any oil contamination. This isn't a surefire diagnosis, but if either of them are contaminated with the other, than it wouldn't be good.

If not contaminated it could still be going into the engine.

On a lighter note...
It took me a few days of screwing around until I was able to find that my coolant loss was in fact a leak. As I never saw a puddle or anything wet, I too assumed I was burning it in my engine. Hope you just have a leak like me!

Let us know.