Can I wear my retainer after 2 years?

I had braces for three years and had them taken off two years ago. I wore my retainer as told and my teeth looked perfect and straight. I stopped wearing my retainer about 8 months ago and had no problems. Last week I put my retainer on as I was worried my teeth may move over time. Now some of my teeth at the bottom have moved slightly out of place! They were perfect before I put the retainer on last week. Should I start to wear the retainer again or should I just leave it and throw them out?