I haven't worn my retainers in a while, can I put them back in without damaging my teeth?

You can wear your retainers, they won’t be able to cause damage. They can move your teeth if worn 18-20 hours/day. The initial discomfort subsided after few days. It’s the pain associated with moving teeth, just like with braces. Depending on how much your teeth have moved, they may or may not go back to perfect but will get better. After 4-6 weeks of wearing retainers full time, you can start cutting back and eventually only wear retainers at night.