I have pain in the arch of my right, what ca. It be?

Pain. I'm assuming is right foot arch could be plantar fasciitis. Common with flat feet. Strench your arch by leaning forward, do towel roll with your toes (towel under your foot and try to roll it with toes) do not wear high heels, use high arch shoes.
Plantar fasciitis. Pain in the arch is due to collapsing arches. Your foot may need more arch support. The pain is due to the overstretching of the ligament called the plantarfascia leading to swelling and pain. Treatment includes ice, nsaids, stretching, orthotics, shoegear change, physical therapy.