For the past 2 days my vaginal opening has felt swollen and sore, and slightly itchy. Today some kind of fluid came out of it and got my pants wet, like I had spilled water on them, and I noticed when I went to the restroom, that there was a LOT of w thick like stuff all over my vagina lips, and the opening of my vagina was very wet. What is this? Yeast infection? What could have caused this to spring up so suddenly?

Yep, sounds like a yeast infection. Does it at all smell?

Antibiotics can cause it in a heartbeat.

Tight fitting clothing, not enough air, sweaty clothing can also cause it.

No it doesn't smell at all, I was takeing some antibiodics a few weeks ago for a sinus infection though

So, very high probability it's a yeast infection and you could treat with OTC preparations. Yeast Infections | Ask a Pharmacist | Pharmacy | Walgreens

Yeast infections can be yucky.

Next time your on potent antibiotics, go to a health food store and get some Acedophelous (spelling), but it's in the link. In good stores it requires refrigeration. Also take cranberry juice. Both a are suggested in the Wallgreens link although they don't directly recommend the capsules. Yougurt with live cultures can work too.