Hi Kate,
Indigestion does occur for some people taking metformin, just google metformin and indigestion and you will see that lots of sites list this.
The metformin is to help lower dad's blood sugar readings and also protects the heart. It is usual to start with a small dose and gradually increase it. If he cannot tolerate it please ask him to go back to his G.P. and ask for the slow release version as this is not so problematic.
Have a good read around the forum and any advice re his diet and blood sugars readings then please ask. There is always someone willing to help.
Regards,
Catherine.