Before you buy any more fish read these articles and find out all the things your fish store isn't telling you.
http://www.fishlore.com/Forum/index.php?topic=620.0
Sounds like they just want to sell you fish and don't care whether they live or not.
a 2.5 gallon tank isn't really big enough for fish, maybe a couple of shrimp.
Sorry you've had such a horrible introduction to fish keeping, it can be a wonderful hobby.
Welcome to FishLore!! We will help anyway we can.
Carol