Pain/inflammation/swelling in ball of left big toe

I noticed some tenderness a week ago, and then just yesterday there was severe swelling, but no heat as in inflammation caused by gout.
I have absolutely no idea how I might have injured by foot.
I cannot put pressure on the ball of my foot under my big toe, and it continues to swell.
The doctor has taken an x-ray, but I can’t understand how I could have injured it without kicking something.
Any suggestions or clues?
Thank you.