It's normal to need more insulin as a pregnancy progresses, but some other possibilities you might want to consider are
1) has your insulin gone off in the heat (if you are using a pen then check it is working correctly)
2) you are coming down with an illness
3) you are injecting in an overused site
Good luck and try not to panic.
Oh, and if you cannot get through to your clinic there is this?
NHS helpline for adults who use insulin: call 0345 123 2399 (Monday to Friday from 9am to 6pm)