Welcome to the site
I hate to give you a rude welcome...but you've got some very, very serious problems with your tank. A single goldfish requires 20 gallons of water, and every goldfish after requires another 10. Common Plecos can reach 2 feet and need giant aquariums. Make sure you are doing water changes every single day with a good dechlorinator...and please look to return every one of those fish ASAP. Once they're returned, you can cycle your tank and choose more appropriate animals to keep. Unfortunately there aren't a lot of options for a 5 gallon tank. It would make a perfect home for a single Betta, an invert tank or a few micro-fish...but right now we need to get the goldfish and Pleco out immediately.
Sorry to give bad news...but this really is a very bad and serious situation