Betta Fishes sickness

Question
Hello, I have a boy betta fish, and he recently developed this bulge under its gills I suppose. I Left for vacation a month ago and left him at a friends house and when I picked him up I noticed the bulge. However This has become bigger. And I am getting worried. I went to PETCO today and one of the employees there gave me penicilin becuase we believe it has something to do with an inside infection and maybe that will help stop it. However I would like to get a second opinion and an actual answer to what it may be. I would really appreciate it, if you would answer back when you can. Thank you and have a nice day.

Answer
I do agree with your PETCO "expert". It does sound like an internal infection, However there are many to choose from, and  I wouldnt know which one. No worries though, it is simple to cure. Make sure your betta is kept at the very least 78 degrees if not 80 degrees while he is sick and I would advise treating with 'Kanacyn'. It absorbs into the betta where the bump is and should cure it. I also would make sure you're doing water changes 2 times a week at least, keeping the water clean.

Good Luck with it, Hopefully that reassures you a bit.

Andy