I'm a runner. my inner ankle bone has gotten larger & is tender after a run. it is not swollen. i have sprained that ankle badly in the past. advice?

Tendinitis? : Based on your brief description, I would first consider posterior tibial tendinitis. Osteoarthritis is another consideration since this can develop years after a sprain. Stress fracture is possible but less likely. In the absence of a full exam and x-ray, I would use an orthotic/arch support, strengthen the ankle with a theraband and avoid running through pain- either rest or shorter runs.