Sounds like it is not cycled, so here is what you do. Get an API test tube kit (or equivilent, but it HAS to be tubes) and remove your fish, preferably take them back to the pet store or give them away (its the best thing at this moment) and get some straight ammonia (pure, non-sudsing), if pure ammonia is not availible (like me) add some food, and it doesn't have to be much, just one algea wafer is enough to send ammonia above your test charts (like 12 PPM or higher). Add the ammonia (or food) so that you have 3-4 PPM of ammonia what will happen is some bacteria will start growing that will convert the toxic ammonia into Nitrites, which is a little less toxic but still toxic. You should see it in about two weeks. However your cycle is still not done, Nitrites are then broken down into NiTRATES which far less harmful, but still toxic if allowed to reach above 40 PPM. If you absolutly have to have fish in your tank, talk to someone else, because its alot more troublesome.