What do you do if you guinea pig is sick and you cant afford to go to the vet?

Go to Petco or Petsmart or any animal store and bring in your guinea pig they will look at it for free and help you if there is something not good you may put it up for adoption or get the correct medicine i have from experience had sick guinea pigs and i ended up getting medicine and it died a month later it might be better to put it up for adoption