Betta problem. Need advice!

My female betta developed this sore on her mouth pretty much overnight. It's not an open sore, just red and swollen. Google searches brought up mouth fungus, but there is no fuzz on the sore/ulcer thing. I didn't have any luck searching on Aquariacentral forum either.
So, I'm looking for some help to identify this and then treat it if possible.

The betta is in a 2 gallon aquarium with just a mystery snail as a tankmate. A tank like this http://www.radiofence.com/products/Aquarius-Hex-Fish-Aquarium.html

Here are pictures of the fish:
http://www.facebook.com/photo.php?pid=357092&l=77314c83ad&id=100000269603326

http://www.facebook.com/photo.php?pid=357097&l=fa734d8ea8&id=100000269603326

Please help, I feel bad for her.

Oh, and thanks in advance =)

I always have 0 ammonia, and 0 nitrites and do weekly water changes to keep nitrates down.

So, I woke up this morning and now she has a serious case of popeye on the side where that sore was. Just great. I removed her from the tank did fullo water change, and am now treating her with seachem Kanaplex. I 'm using bettatalk's guide for this treatment.
Since, I have her in a glass vase it's probably only a gallon or less, should I change the water every day or stick with every 3rd day like betta talk says?

Well, My initial tank is a 5 gallon http://www.petco.com/product/13809/Marineland-Eclipse-Corner-5-Aquarium-Kit.aspx

In it I have 2 mystery snails, 3 glass cats, and had the female.
But on another trip to Petco this plakat caught my eye, and I couldn't leave without him.

So, I got the 2 gallon. I put the female since she's smaller in there and one of the snails just to help clean up. I was testing every few days and besides nitrates nothing else was out of the ordinary. So, I was changing once a week. From what I've read about betta glass vase bowls recommendation of once weekly changes I figured the same would be fine for a 2 gallon.
Apparently not.

Well, I've been keeping her in a separate bare bones bowl altogether. I've been changing the water and adding meds every day. Like I said I am using Seachem Kanaplex and Tetracycline.

She is active, not acting sick, she is eating, but the eye and that sore I first complained about is still nasty as ever looking.

Anyone who has successfully treated popeye know how long is usually takes for this to go away? Other sites I read said that there is a possibility that the eye might even come out of the socket!