Welcome, AlysazZz!
It isn't uncommon to remember dreams in the middle of the day, but it's very interesting if the dream was from 3 years ago. Perhaps the dream was a few days ago and you just remembered it, with the sensation that the dream was dreamt a long time ago, which isn't that uncommon. Dreams after waking up can feel like it was a long time ago. Naturally, like other dream memories, if you don't consistanly go over details of the dream upon waking up, the dream memory will go away.
If you're interested in keeping your dream memories, you should first of all start a dream journal. Upon waking up, you should try not to move too much and just close your eyes while laying there. Some previous dream memories of last night should come back, maybe in blotches and unchronologically. If this is the case, you should try and think through 'what happened after this' or 'what happened before this' and trace back your steps.
Good luck with whatever you're trying to do and i hope you stay around. This community is excellent and full of information.