I work for the digital switchover help scheme and frim the sounds of things you are in the middle of switchover at the moment and that will finish on the 20th and then you should get all the free view channels as itv4 and dave are on groups of channels that are on a reduced power till after the switchover which you will have to retune once again on the 20th and then on the 28th sept if that doesnt solve the problems after the 20th april then you maybe coming from sutton coldfield transmitter. The best way to find out is to see if you still get bbc2 on the analogue.
I hope this helps