Please take him/her to the vet. Eye infections can progress very fast in different species and can harm or blind the animal permanently if left untreated. There is nothing you can buy "over the counter" that is safe to use in this case as the medication is only prescribed by the vet.
Most likely your asking about the inside corner area and referring to your tear duct.
Sounds like a stye
Cherry Eye Disease is something only dogs. The disease starts out appearing as a small red bump that sticks up above the third eyelid and is located in the corner of the eye nearest the nose. Cherry eye is actually caused by an inveted nictitans gland.
What bump are you talking about
what cause bump on eye lids
baby bump!
that's not a bump that's the lens in your eye that sticks out
caruncle
A stye eye is a small, reddish bump on the eye's lining (usually where eyeliner is applied on the bottom of the eye). Sometimes, it has a white tip.
herepes.
A stye eye a small, reddish bump located on the eye's lining (where eyeliner is usually applied on the bottom of the eye). It is caused my oil blockage in the eye or the effect of dirt that wasn't properly cleaned out of the eye.
Guinea pigs sometimes get small bits of hay in their eyes and this is not harmful unless the hay is stuck in the corner of the eye. Larger pieces of hay could hurt the guinea pigs eye.