If your not finding antifreeze (radiator fluid.
) puddles then it sounds like you do have a head gasket leak or a cracked cyl head.
Defiantly replace you radiator cap and fill your radiator up. Also when you do get the radiator almost all the way full squeeze your upper and lower radiator hoses, with the cap off, to see if you can get any bubbles out (trapped air).
Check it the next day after driving, while the engine is cool, to see if it needs topped off or if you've lost any antifreeze. DO NOT WAIT ANOTHER WEEK.
Also check your oil to see if there is water/antifreeze in it. It will look soupy and white in color.
Also look at you exhaust while the Tj is running. Does it look like steam is coming out your tail pipe? If so the you've got a problem.