top of foot pain - extensor tendonitis?

Hi! I’ve been training for the NYCRuns Brooklyn Half the past few months and ~2 weeks ago started having pain along the top of my foot (possibly the extensor tendon connecting to the big toe) with walking/running/activity that has not subsided the past 2 weeks (despite not having run since the onset of pain). No trauma/incident that brought it on. Bump on top of foot and slight tenderness to touch. Pain on top of foot and on tendon on the top of my big toe with each step while walking/running, as well as when I pull toes up to flex the foot. No pain just standing and X-ray came back clean.

I started wearing orthotics a few months back b/c of arch pain from flat feet and know it’s not shoelace imposed.

What should I be doing at this point to help ease pain/heal/rehab?

Moving forward, how can I prevent this from occurring again?

Would appreciate any help 🫶