As you read from the answers to your post, please don't give up! We all lose fish, especially when we started out, so be brave. I'll just add my two cents -- get a bigger tank (you can get 20g at most yard sales [because someone else has gotten frustrated and given up]), this will allow you to get rid of the incandescent light (which plays havoc with temps) and select just one primary species of fish.
Val
Val