Jennie,
I agree with everything Mr Bump says.
It sounds like a cartlige problem to me but as others say you need to get seen by an expert (not a GP).
I'd also google itbs and get this checked out also to make sure you've not got Illiotibial Band Syndrome which can often be confused with a cartilidge problem if the pain is on the outside of your knee.
If it is the cartlidge i'd suggest that a physio will also be of little help at the moment (physios feel free to contradict / agree as appropriate) as if it is a cartilige prolem then I'd imagine you'll need an operation (Arthroscopy) to get it sorted following which a physio will be invaluable.
The GP should refer you to a Consultant Orthopedic Surgeon who will better be able to assess and hopefully rectify the problem, waiting 4 weeks for this to happen will only prolong things as there may be a bit of a wait once you've been referred.
I had this problem a couple of years ago and had the op (luckily I get BUPA through my work). After afew weeks recovery I got back to things and now have no real problems.
If you also search arthroscopy in the keyword search at the top of this page you'll get other peoples views as know others experiences are not as positive as mine.
One final point is that if you can get referred to a Surgeon or Physio who runs themselves you'll find them much more positive and will offer greater assistance than a 'non runner'. This can make all the difference.
All the best and let us know how you get on.
Ali.