severe red streaks, pop eye, and tail rot...

Hi everyone,
I sure hope someone can help me with this because I don't know what else
to do for my sick goldfish. This fish is about 4 years old and has been
living with this condition for nearly a year now. This fish has big red
(blood?) streaks going from it's body all the way down to the end of its
back fin in a few different places. It is so severe at one point that it is
splitting its fin and the rest of the fin looks all raggedy. It also has a
case of "popeye" on it's left eye. The right one appears to be normal. I
bought 4 "feeder" goldfish 4 years ago to help me get started with my tank.
I have two of them left, this one that is sick and a healthy one. They have
gone from those tiny little things that you see in the "feeder aquariums" at
the pet store to medium bluegill size (about 5 to 6 inches).
I have tried those tank buddy tablets, some kind of capsules that
contained medicine strickly for goldfish disease, ick medicine, and some
other kind of liquid stuff that was recommended to me by a local pet shop. I
can't seem to find the right medicine to help this fish.
It will rest on the bottom when nothing is "going on" in the tank, but it
still eats like a champ, swims around to get the food OK, and it's poop is
of the normal brown variety. It does droop it's fins when it is resting on
the bottom but perks them right up at feeding time.
I have two bottom feeders (small catfish type) two other small goldfish
(my son just won from the local fairs) and a betta. I don't want to harm any
of them in the process of trying to treat this goldfish. To tell you the
truth, I'm surprised it is even still alive. I just think that since it is,
I owe it to the fish to try to help it get better. Any advice that you may
have would be helpful since I really don't have a clue what to try to do for
it anymore.
Thanks, Cindy