It's been really cold the last few weeks, like -20C, but recently it's gotten up to 10C. I don't know if that has anything to do with it but When I was leaving work last night I went to stop at the gate and I could barely stop the car. What would have normally done it was barely affecting the speed so I had to push really hard. I then did a few stop and go tests in the parking lot and everything was fine.

This morning I went to take my brother to school and the same thing happened the first time I pressed the breaks. Right after I let off and press them again the brakes work perfectly fine for the remainder of the drive.

I checked all my fluids and they are at or just below the max lines.

I have been given the following suggestions so far:
Air in the lines
Bad seal in master cylinder

I'm not sure how air would just magically appear in the line all of a sudden, maybe it was always there and just now worked it's way into the line. I'm thinking more along the lines of a leak somewhere.

When was the last time you changed your break fluid? It could have a bit amount of water in in now and its making it spongy.

^^ agreed, you could've gotten water in there, and the water would've frozen at -20C but could be melting now that it is getting warmer

If its is the master, it wouldnt be air. It would be that its just leaking internally and feeling spongy.

I would:
Bleed brakes and replace fluid
if its still there, master

Should cost 20 bucks to replace it all if you do it yourself. And a little work. Master cylinder replacement isnt bad either.

if its the master cylinder it should just be a fluid check ball gone bad or bad seal, you could just get a rebuild kit for it, pull it apart, and put the new seals back together... shouldnt be that hard

give each of your calipers/brake lines a quick once over with your hand. just reach behind the wheel and make sure your hand doesn't come out with brake fluid on it.

weird it just happened all of the sudden.