Hi, I am really sad to hear that you have been having a disastrous time with your fish.
First thing would be to check the temperature of the tank and make sure it is alright. And that the filter is working and the fish have air. From the filter or an air bubbler.
Then if so, do you have a test kit and can tell the parameters of the tank?
How long have you had the fish?
Did you add new fish or plants into the tank recently?
How long has this tank been up and running?
If you did a water change did you add dechlorinator to the water? Match the temperature.
Do you know what the pH is? Sometimes you can have a pH crash if you do not have much calcium / KH
/ Alkalinity. And how much did you change?
When did you do your last water change?
So doing some pwc
's might be helpful if the tank has unsafe levels of ammonia, nitrIte or nitrAte.
Sometimes a sickness from a new fish could be a problem.
Or if it has been a pretty long time between water changes.
Or, if in the last week or 2 you threw away the filter pad and added a new one.
There is a good article in my signature you can come back to later when you have time to read it, about aquarium keeping and the nitrification cycle. Good bits of information.