There is quite a long list of medical problems that would stop you diving. This include, but are not limited to :-

Middle ear problems.
Lung problems.
Certain types of Astma.
Certain types of medicine use.

If in doubt consult a doctor at a hospital that has a hyperbaric chamber.

Sinus problems are a direct contraindication to diving due to the inability to equalize pressure while descending. Any pain while descending will only intensify as you go deeper. To stop this simply come up to a shallower depth and equalize the pressure in your ears. Bottom line is if you have a sinus infection don't dive even if you are taking medicine for the problem