Well, for your case, I have to say that you may get eye infection because of the eyelash extensions. First, you should know that these fake eyelashes are applied to the eyelid and then removed after usage, and eyelash extensions are applied directly to the natural eyelash with a bonding agent. And they are made of chemicals. So they can carry some bacteria in your eyes and even lead to some eye disease, such as the eye infection, red eyes. That is why your eyes hurt. So I will not suggest you use eyelash extensions too often.
Well, it seems that there is something wrong with your eyes as a result of using eyelash extension. I quite understand your puzzle and question. So, as a matter of fact,your eyes are painful because the eyelash extension is an irritate stuff made up of chemical materials, which could lead to some bad feelings, even pink eyes. So, you should make better use of your extension and take care of your eyes.
The eyelash extension contains the stimulating materials which will irritate your sensitive skin. If your eyes feel hurt, you'd better stop using it. Or else, your eyes may get the infection. What's worse, your eyes may get hurt. You should use some eye drops now to release the light symptom.