I sprained my ankle the 21st. X rays on the 26th (not broken).Dr said I could work 9/2. Work 12 hours on my feet. It still hurts and is a bit swollen?

Ouch. Sounds like you'll need to call your doc to update them. Perhaps you need a few more days off to rest the ankle. Keep taking your anti inflammatories for pain and alternate ice with heat. May want to elevate your leg while sitting and consider an ace wrap to help with swelling.
May last a long time. Swelling may last a long time following a foot or ankle injury. An x-ray can show if there is an underlying fracture. The x-rays may be falsely negative initially in cases of small stress fractures. You may have a soft tissue injury if it is just a sprain and may have damaged the muscle, tendon, or ligaments in the area. Have it evaluated by a professional and get the appropriate treatment.
Soft tissue injury. There are many tendons and ligaments in the foot and ankle. They can be strained or torn but this is not seen on an x-ray unless there is an associated dislocation.