So I replaced the brake pads about 4 months ago and I noticed the passenger side was barely worn while the driver side was down to metal on metal, is there anything beside replacing my caliper? Note: I have a bad proportioning valve but I'm not sure if that would have anything to do with it?

When you changed the pads, did you notice if the rubber seal around the caliper piston was damaged? If water gets in there it will rust the piston and it won't move. Replacing the caliper is the only real option.

I did not notice it at the time, well the passenger side seems to be fine, do I have to replace both either way?

If one side is working fine, then no real need.

Also check the sliders and the boots around those. If those boots get damaged or if the sliders go dry, they can seize up. It happens a LOT on 1st gen w-body rear brakes.

on my 94 my pass side front caliper kept''sticking'' and covering my white car in black dust so i took the sliders out and greased them lightly..along with a small amount of filing with a half roun file and never had a problem again

I replaced both calipers for like $70 or so each, and then took the old ones in for the core fee. In the end it cost me around100$ for new front calipers and brake pads.
Just saying

Often times, if its the sliders and/or slider grease boots are bad, they can all be replaced for around $25 for both sides. I would only advice replacing the caliper if it is absolutely necessary and you are 100% sure that the piston assembly is at fault.

I had to replace a caliper recently. I needed to bleed the brakes, and the bleeder bolt broke off inside the caliper as I was trying to unscrew it. I tried a reverse drill bit to get it out, and the reverse drill bit broke inside the caliper. I didn't really have an option there.

The calipers on my 95 Regal are 226k miles old and I've been able to keep them working properly by inspecting or replacing the grease boots, pad shims, sliders, and bolts (if necessary) every time I replace the pads.

Best way to tell if it'* sliders of caliper is to look at how the pads and rotor is worn. A stuck slider will have one very worn pad and half the rotor will be worn more then the other. A bad caliper may even have rust on the rotor because the pads simply don't contact the rotors very much.