How often do you add coolant to the resevoir?
 

It seems I add coolant on a regular basis. Not sure what constitutes normal but I'd say every few weeks or so.

How about you guys?

Never

Also want to add, there are no visible leaks anywhere. I don't know where I'm losing coolant requiring me to to add it frequently.

My guess would be the water pump if it has never been replaced, they have a weep hole and if it is starting to go it might not be enough to really see it happening. That or watch your transmission fluid and engine oil very close as both have in radiator coolers and have been known to rupture. If it is just enough to drain the overflow tank every few weeks it is probably a tiny enough leak that it just goes away when hot and driving which will make finding the leak a bit harder.

check your clamps. i was loosing a bit and found the culprit to be there was 3/4 of a factory clamp left on the upper radiator hose at the thermostat housing. but missing coolant has to be going somewhere if not on the ground its in your engine oil, transmission or blowing it out the exhaust. the water pump you would see on the ground or on the skid plate.

X2!!!

Thanks guys. Gonna have it checked out, can't find any signs of leaking.

There should be Zero loss. You 100% have a leak.
The answer is very simple, even if you do not see any fluid on the ground.

You are either:
1. Burning it. Leaking into the cylinders. Usually un-noticeable unless it is a lot and then appears as white exhaust.
2. Emulsifying it in your motor oil or trany fluid. Sometimes hard to tell in motor oil if only a tiny amount, as it evaporates from the oil and goes out the crankcase or is reburned.

And this is the most common cause:
3. Tiny leak somewhere on a hot engine.
It evaporates before it drips. If you smell antifreeze, you know you have a leak.
Some people can not smell antifreeze. I can smell it from 50 feet away.
Look for whitish or yellowish streaks down your engine.
It can look like old yellowish toothpaste. It is hard crumbly stuff. You can see it sometimes on the end of rubber coolant hoses if they are weeping or spongy.
That stuff is the dried glycol and additives. And pinpoints the leak.

Let us know what happened.

I would have to agree with the general consensus, you have a leak, this could be a number of problems, gasket problem, head gasket, issue.. When I first got my 06 I fully flushed the coolant system then refilled, the level never changed from that point for a number of years.

First look for an obvious leak, water pump bearing/seal, coolant lines, hoses, heater core, etc, then check engine oil for contamination with anti-freeze, check transmission fluid for the same, if all of these prove fruitless you can get an HC/Antifreeze tester to see if you have a possible head gasket problem.

You need to identify the leak as soon as possible, don't let this go on as serious problems could result depending on the issue.