Could the arch pain in my left foot be caused by a bump on my tendon? what could it be?

Plantar Fibroma: Lumps on the bottom of the foot could be a condition called plantar fibromatosis. Essentially it's a growth on the plantar fascia. I would recommend evaluation by a podiatrist.

Many possibilities: Some causes of painful “lumps and bumps” may include: bony overgrowths, soft tissue masses, ganglions, fibromas, and cysts. Have it evaluated by a professional to get the right diagnosis.

Plantar fasciitis: The bump can be a plantar fibromatosis caused by overuse injury to your plantar fascia ligament. What happens is the plantar fascia becomes so tight it has micro tears, then your body is trying to repair it, it scars and forms a nodule. The best way to treat it is to keep the pressure off the nodule with orthotics, padding, wearing comfortable shoes. Stretching, ice and steroid injection can help.