I haven't worn my retainer in a month, after getting my braces off. Do I have to worry?

Not wearing your retainers for a month is not a good idea if you want to maintain straight teeth for the rest of your life. The good news is that you have plastic retainers which will act as clear aligners to straighten your teeth in the event of minor orthodontic relapse. If the retainers fit comfortably and completely over the teeth then you probably had little to no relapse and should have nothing to worry about.Good luck! 

Throughout our lives, our bodies are always changing -- this includes our teeth. The teeth have a natural tendency to shift over time. Retainers help to keep them in the position they are after the braces. If your retainer still fits in well, this is a good thing. If it is tight when you put it in, this means you need to wear it more often. I would try to wear it a few nights a week to be on the safe side. The problem with wearing them once a month is that you may forget to wear it for 2 months, then 3 months and then one day when you try to put it in, it may not fit anymore.