Take a breather for a minute. Getting started in the hobby is always a
little stressful - especially if you care about the fish you keep, and
you obviously do. That's not a reason to give up. You've learned a lot.

Try starting out a little slower. Do you have any fish left? Try only
keeping a very few fish to start with - something like an inch of fish
per 5 or 10 gallons. That will give you lots of room to make mistakes
without hurting your fish. Then you won't get so stressed out and you
can learn and build up the knowledge to keep more fish.

If you are keeping very small fish and the filter seems to be giving
you problems try replacing it with a sponge filter. You can buy a
decent sponge filter for about $5 so you don't have to worry about the
cost much. And as long as you're only keeping a few easy fish a sponge
filter will be completely adequate for nearly any setup. It's even safe
for the smallest fry so you won't have any worries.

Since dying fish obviously stresses you out be careful to select a fish
that won't die easily. Stay away from guppies - yes they are easy
beginner fish but they have short lives and tend to die off quickly. I
don't think you would like that much. Try something longer lived. How
big is your tank? If you have a 20 or 30 gallon tank you might try bala
sharks, very easy and fairly long lived. If your tank is a 10 gallon
then try something like a couple of cory cats, or several danios.
Something small and hardy. Don't get tetras of any kind, they're much
more liklely to die than most other small fish. Just take it easy and
start slow, when you get more confident in your abilities then get more
fish.

And while you're selecting your fish go to the plant section and buy
either some hornwort or some anacharis and stuff it in your aquarium.
Those two plants grow easily and quickly and will provide a buffer that
will help control the water and give you a little extra time to react
to ammonia spikes and such.

Your fish will be ok.

-Daniel