Being an '02, it could be as simple as a recharge on your regfrigerant.  One
of two options would work for you.  Either stop by an Autozone and pick up a
recharge kit for $20 or so, connect it to the low pressure port, which
should have a grey cap with an "L" on it, or pay God knows how much to your
dealer or an AC shop to recharge it.

The recharge cans usually have the oil and cleaner ingredients, too, so you
should be good to go in that sense.

Did that on a few of my vehicles here in very humid southeast Nebraska, and
it works like a champ, but Houston has a much longer term of AC use every
year than we have, so that could be why its run out that soon.

The nice thing is, on vehicles built after 1990 or so, most of them don't
let the compressor fire up if the charge is too low, so you won't damage
anything, theoretically..