Small blister like bump in the eye.

Hi, I don't have any glasses before. I feel some kind of dull pressure in the top of the right eye. Only on the side of the nose and top of the eye.not on the bone. Just on the eyelid. I had a annual routine check up and OD said everything normal and prescribed glasses for me for my minor astigmatism. I see some small bump like blister which is on the edge of the right eye. I don't have this on the left side. I have this for several years. But the dull pressure like feel on that eye is from last 2 years. Checked with doctor twice and said no issues. What is the small bump thing. I have this for several years now. It's on the edge of the eye. Size doesn't change to bigger than this. Sometimes it will be smaller than this and not bigger. OD said it could be fluid present there and he is not sure about it too. He want me to see another specialist for that. What it could be? Is it something serious? Whether this could cause dull pain on the same spot on the eyelid? pls help. thanks!