Can my foot injury last longer than I was told or if there could be a more serious injury?

Yes. Sometimes xrays could miss a subtle fracture or soft tissue damage such as ligament tears( lisfranc), tendon tears or cartilage damage. A good clinical exam should detect this but at times a MRI or ct is needed when injuries last longer than they should on a compliant healthy person. Ask your podiatrist if there is anything else that can be done or seek a second opinion.