Screwy Beta

Question
I have a Beta in about a 2 gallon round tank.
Has rocks and one aquarium plant.  I have had the fish for about 1 1/2 weeks.
When I first brought him home he showed signs of stress.  But within a couple of days he was coming up to the side of the bowl when I would sit by it and swim back and forth.
This evening he has be swimming really weird.  I guess you could say spastic..Not smooth and graceful like he has been.  He has actually been laying at the bottom of the tank under the greenery on his side.  Occasionally he will come out and swim up to the top take a big gulp and then just hang out at the top almost vertically.
I have been feeding him once a day.  Fish flakes right now until I can get to the pet store to pick up some bloodworms.  
He doesn't seem overly intereted in the flakes.  Occasionally he will eat them.  
I have not tested the temp of the water and I have no idea what the ph is.
I do not use tap water.  I actually have been using bottled water.  NOT distilled.
Anyway, I am hoping that maybe this is just something that these types of fish do but if not any help in figuring out what is wrong would be great.
Before I forget.  I have changed the water once so far since I brought him home.
Thanks

Answer
Hi;

I think your fish is showing signs of stress and disease. The page on this website has information about treating fish illness. Also there is a lot of helpful information on this site about keeping fish and Bettas. Copy and paste this address into your browser.

http://www.aquariumfish.net/information/recommended_treatment.htm#top2

I hope this site helps answer your questions. If it doesn't please let me to and I will try and help.
Best of Luck,
Emily