Problem keeping him hard...

If you have any history of cardio problems or diabetes in your family history you need to get checked out by a doctor, who may try some remedies or refer you to a urologist. I understand that one can have blockages that impede the blood circulation to the penis. This may be an early warning sign of future cardiac problems if ignored. Medication and a healthier diet may be part of the solution.
Go to any walk-in clinic, if you are uncomfortable seeing your doctor. They may refer you to a specialist if a medical cause is suspected, otherwise they can prescribe Viagara etc as a possible solution.