Hi Clare, do you feel bloated when you run, like you have to go to the toilet? Also, how long do you leave between eating and going running? Avoid having a really heavy breakfast - light cereal, banana, yoghurt will probably suffice (try and take in about 350 calories for energy), and a snack before lunch (depends on when you start work and when your lunch is so play this by ear) BUT try to avoid eating an hour or so before run.
Also drink plenty of water. Let me know if this works. A lot of things about running as we are finding out is trial and error!