Discussion: That's not good.

Maybe you should take tomorrow completely off (no ultimate, broom ball, running, etc.). If it feels okay, you can test it Tuesday but only on GRASS. IF it's not completely better, you should probably take Tuesday and Wednesday off too.

Much better to scrafice a few days now than to be really crippled in another week.

Definitely not doing anything tomorrow. Melanie said it's probably the meniscus, so I'm going to do lots of stretches and strengthening for the surrounding muscles in the mean time. Currently I have crossing my legs and bending down both in front and to the sides for stretching, then one-legged squats and biking for strengthening. If anyone else has ideas, shoot them my way!

Well, my idea would be don't do anything. All the stretching and strengthening is just going to aggravate it. If you want to do that stuff, fine but WAIT till it's better. My experience is that stretching/strengthing something that is injured does NOT help it get better but only prolongs the recovery. What works best is to NOT stress injuries. Let them get better first.

The exception to all this is ankle sprains where I think continuing exercise is the best approach to healing.

Another thought----Try using the elliptical exercise machine and see if it aggravates your knee at all. If it does, don't do it. But if there is no pain whatsoever, than use it for 30 minutes or so. It is very similar to running but no impact and that's important. Remember Florian Schneider used machines a lot prior to JWOC 2013 to keep fit and avoid injury.

Outside of knee could be IT band. Is your hip tight?

Hips are fine. Everything else is all good.

I think Brendan and your dad have good points. Does not sound like a meniscus issue unless you really twisted it bad on the run. I would rest it it, stretch it out, especially your hips. Supper tight hips sometimes don't feel tight because your not aware of the smaller muscles inside the joints that pull on everything. Take a warm salt bath keep the area warm. Conventional medicine would say ice but it really does not not work for tightness. Make sure your eating is good and not a ton of candy, muscles seize up when they don't have the proper nutrients. Keep and eye on it. Another cross training is pull running or the nordic track. Both are good if you can do it pain free.

What are some stretches I can do, and what's pull running and nordic track?

This sounds similar to my IT band problem. I didn't have any pain in my hip, but my knee hurt. Do a few one legged squats on the knee that hurts and see ff you knee wobbles back and forth a lot. I would also use a foam roller. Mine should be at home somewhere unless you have already grabbed it.

Foam roller is a good idea. One of the few things I didn't steal from you yet...

The crossed-leg stretching you're doing is the standard recommendation for IT band syndrome. Like Andrew said, you may feel nothing at all in your hip, but it's good to stretch that out and also the glute and lower back muscles that connect to it. Another good stretch is to lie on your back and cross your legs so your left ankle rests on your right knee, then pull your right thigh towards your chest, and hold that for a minute or two as the muscles release. Good to repeat on the other side, too, obviously.

If it's ITB stuff, foam roller is magical. It takes 10-12 weeks of stretching for 3+ min/day to see any actual gains in muscle fiber length, but foam rolling and massage can loosen abnormal muscle adhesions almost instantly.

Totally agree. A week after debilitating IT pain I was able to run a half marathon, fast (for me), with no pain, because I was vigilant with the foam roller and stretches mentioned.
Good luck.

Unfortunately I won't be able to grab a foam roller for a few days, but once I grab it I'll be hitting it hard.

Oh, and KT tape. Miracle stuff.

Use a water bottle then. Or a wine bottle. Or anything that's round.

Where would I, a 20 year-old college student, obtain a wine bottle?

A frat's trash bin. Or recycling if they're the progressive sort.

That's... not the worst idea I've ever heard.