Why does my left eye sting & burn?

I've been a contact lens wearer for about 7 years now. For the past 3 years or so, I've noticed that my left eye has been getting irritated whenever I put my contact lens in. I assumed it was maybe lint or hair in the lens and tried washing it but the stinging is still there. I've changed contact lens brands to Air Optix, my contact solution and rewetting drops and the stinging and burning is still there! I came to terms that I probably have to live with it but it is so annoying! Even when I'm wearing my glasses, it feels as if I have an eyelash in my eye or it burns as if soap has gotten in my eye and it is horrible! Does anybody have a clue on what the hell is going on with my eye?!