I am 24 and have been experiencing pain in the back of my right eye. No pink eye or stye present. No sinus infection. Ideas?

See ophthalmologist. Your vision is too precious to fool with and you should make very sure very quickly that nothing is going to damage your eye. Following that, if nothing is found it may be necessary to have an MRI with thin orbital slices done with contrast to determine if there may be a tumor in back of the eyeball. Please go and get evaluated soon.
It is best to ... . Have an eye exam, pain can be f rom many things ranging from a tumor or inflammation or even dry eyes.