I Have Been Getting Little "pimple Like" Yelowish Bumps On

I have been getting little "pimple like" yelowish bumps on my upper and lower waterline of my eyelids. Usually only 1 or 2 per eye. They last for years. I had 1 on each eye awhile back and popped them. Its very hard and painful to do. They went away afterwards. I haven't tried to pop the 2 I have on my left eye now. Had them a couple years now. They don't go away. I hate them. What could be causing these? A what could they be?