What causes pain and swelling in the instep of the foot?
If you're suffering from this pain, Patd, you have my sympathies. I've had problems with my arches for years because of poor shoes choices, and I know it can be a miserable thing.
Pain and swelling in the instep can be caused by many factors, including overuse, poor arch support (which caused mine), injury, or a disease such as arthritis. Only a doctor can evaluate the condition that's causing the pain and how to treat it.
In the meantime, here are some links you might find useful while you're dealing with this condition:
Why Yoga May Soothe Many Types of Chronic Pain
Over-the-Counter Pain Medications
Five Drug Combinations to Help Chronic Pain
Best of luck to you!