I have a Blackberry Curve and from last night and alot today it has been deleteting my Facebook notifications and if a new message appears other notifications disappear and has been deleteting alot and has gone up to the 1st January and I have no idea how to stop this anyone help?

you may have a setting wrong of simply too many messages on the BB.
Messages are considered the same as email.

KB10183-Email messages are deleted from the BlackBerry smartphone before the "Days To Keep Messages" limit is reached 0 2001486202

How can I change the settings if need to or will it just be fine on it's own and get back to normal?

What model Curve do you have? There are many
What OS are you running?
When is the last time you did a Battery pull? << 1st step to take if device is having problems? - BlackBerryFAQ

Reading over your owners manual will tell you how to adjust the retention settings.

Do you have two many messages in your account?

I have no idea what kind of Curve it is my box is stored away somewhere never taken the battary out before. Mebre I do have too many messages because when I first got it it had aleady stored my notifications

If you never delete messages it could simply be out of memory and dropping the oldest.
You need to understand the blackberry has a limited amount of memory. Also it may help if you go to the blackberry web site and read the information on your model.
The model is available in the battery compartment.