Pictures do not show up in camera roll, but are on phone.

My iPhone 3G has recently started playing up when I take pictures. I can see the last picture I took in the little box on bottom left whilst taking pictures, and on the main photo library bit where it says in brackets how many pictures are within that album it includes the ones that I have taken, but when I open the camera roll they are not there. But then when I plug my iphone into my laptop the pictures come up in iphoto and i can transfer them.
Does anyone know how to fix this problem as it is annoying that I cannot look through the photos i have taken nor upload them whilst on my phone or picture message them.

Thanks
Shauni