I've had calf pain in my left leg for over three years now. no swelling or redness but it hurts to walk on. could this be a dvt after all this time?

Unlikely: I will do the never say never but highly doubt this is from a DVT - would expect swelling if there was a dvt. It is not impossible though.

Probably not: Dvt classically result in swelling +- pain (from a little to alot). Post -dvt syndrome can hurt for years after the DVT has resolved. See a doc ( vascular md if you are vry anxious about a dvt) and look for other causes