For the past while my Blackberry Curve 8250 has really been acting up. It's really awful. It's very slow and takes a few seconds, sometimes, for it to register what you've clicked/scrolled the touch pad. When playing music this is very annoying in particular.
The battery seems to also be a huge problem. It runs very, very quickly. Less than a day. I haven't timed it but I'd say it lasts about 7 hours. I always used to use it as an alarm in the morning and can't now.

I really don't know what to do- have I got to replace my whole phone? I only got it at the beginning of summer last year- I ordered it online from Vodafone.

Sounds like you have multiple issues. The easy one is the battery. If you let it run down below 20% it wont recover. ALL cell phones use LI type batterys and this is a big issue with all of them. Replace the battery would solve this issue. The bigger issue is the key pad. If you ever got it wet or dropped it it may be the problem. Almost nothing can be done except a repair or replacement.
The other possibility could be low memory caused by too many third party apps. Any idea if it was wet, dropped or has low memory?