Sorry you're having problems with PMs, not within my ability to check what's going on but I wanted to let you know that there are two PM systems that the Flytrapcare.com forums utilize; both should send you an email (via the email address you registered with) when you receive the PM though.
It may help to ensure that you are signed into the community section of the website as well as the forums. Both segments use the same log in data.
http://www.flytrapcare.com/carnivorous- ... unity.html
It might be worth emailing Matt or Steve (or... PMing them) if you continue to have problems, they may be able to check server-side just in case something has gone awry.