What's wrong with my poor betta?! His belly exploded over a 9hr period!

Today when I left for work, my betta looked something like this:

http://x30.xanga.com/3a4b5a013713041.../m28326630.jpg

When I came back from work today, he looked like this (the photo is a
bit blurry but I think you get the gist):

http://x78.xanga.com/922b40fa63d3144.../m30002234.jpg

I was told that this was a male, so I don't think it's eggs. What is
it?! It just happened over the course of one day! He looks like he's
about to explode even though he appears to act normal. His coloring
seems about the same and I just did a water change 5 days ago. I don't
have anything that changes the pH or anything like that, but does it
matter that I started feeding my cories in there alpha wafers? Would
that make him sick? Any ideas?!