No 3G signal on iPad 2 wifi + 3G
I have an iPad 2 wifi + 3G with an O2 sim card. I only have used mobile data on my iPad a few times when away from home. The last 2 weeks I have been all over England and cannot get any 3G signal. I have got over 2GB of data left on my account. At the top of the screen it shows 5 bars with O2 and only ever shows 'E' or 'O' no 3G. I have an iPhone and the places I am using the iPad has 3G signal and O2 have also confirmed I should have good 3G in the areas I am. I put the sim from the iPad into my iPhone and can get 3G so it's not the sim card. I am running OS 5.1.1 and have the latest carrier settings. Can anyone help me as I can't find a similar post anywhere online.
iPad 2, iOS 5.1.1