I was just renewed my licence this year, but the time before that I had a similar wait to yourself, on ringing the DVLA they said they were doing some medical checks and that was the reason for the delay, however the chap on the phone said not to worry as if I didn't here back before my licence had expired I was still OK to drive, he said something about a regulation that allows people to drive if the DVLA haven't conducted their investigations before a licence expires.
So if the DVLA haven't told you you can't drive you should be fine.