Help porter!?

my dog, his name is Porter, he's a beagel. anyways...every once and a while he gets this red bubble looking thing on his eye and it's always the same eye. it will last for a day or two then go away all on its own. i would take him to a vet, but like i said, the thing will go away in a like a day, and my mom always puts it off and says that she doesn't have the money. but this dog is like family and i dont want this to be something bad that we just keep brushing off. also it looks like it would hurt but he doesnt seem to mind. does anyone know whats goin on?