I have hot water in the kitchen and bathroom sinks, but the water in the shower never seems to get hot. How can I fix this? :(

Please tell us about you shower valve, one handle or two, brand and model if you know them? The problem is likley in this mixer.

I can't remember the brand (but I can find out when I go home tonight), but it only has one knob as well as an adjuster between "tub" and "shower".

I think the adjuster is actually the diverter knob. Sounds likely you may have a cartridge mixer and the hot side is plugging up with debris. How is the hot water in the tub, the same as the shower?

The water in the tub is the same luke warm temp. I just bought the condo in April and they redid the whole bathroom before I bought it. I didn't think about it much over the summer because luke warm showers were nice, but now that it's getting colder outside, I look forward to hot showers in the morning (and dread what I'm getting now!).

I think your mixing valve, the lower handle, is getting plugged on the hot side. Can you find the main incoming line and shut it off? After the main is off open a faucet to blow off pressure, remove the knob and the escutcheon (plate thing). You should see a nut like ring about the size of a 50 cent piece or a plate with 2 or 3 screws in it. Remove which ever you have and pull out the cartridge assembly. Inspect the bottom side for the inlets. I think you will find white crud in the inlets. Pick it clean with a tooth pick and blow through it with your mouth while opening and closing the handle. Hold a towel over the open valve and have someone else turn your main on and off quickly, this cleans out the pipes a bit. Reassemble and you should be good to go. F you need more details just let me know. There are several here who can help.
Good luck.