Can anyone tell me how to access my pm?

Normally you need to be VIP to send and receive PM's however.

I think escorts get a limited form of PM, but I'm not quite sure how that works.

you can check at the top where it says mail.
VIPS and providers get that feature. It seems that you are a provider but you can only have access to PMs if your reviews are linked to your username.

contact TER and ask to link your username to your review/s providing your ter id and as soon as they do it you will have access to PMs!