Do what Screamapillar says and read through these forums.
A lot of beginners have come here after making errors at the outset. If I had come here first I would have been saved from shin splints, aching calves and knee pain.
Running for distance involves a lot more impact than running as part of a sport such as football. Good technique and starting gently can allow you to build up with less chance of injury.. There are some pretty decent books around which detail technique, I like Chi Running for this, the mystic east stuff is a bit beyond me, but the philosophy of aiming to run without injury is spot on as far as I am concerned.
Changing your diet for a couple of weeks isn't going to make much difference, but healthy eating is a good idea, if you aren't doing it already. Radical changes in diet can be a bit of a shock, so maybe look at it and make changes gradually.