Edelweiss

With plantar fasciitis the pain is usually in the arch or heel area. I'm not quite sure where the "inside of your left foot" is. If it's in the ball of the foot area, it could be a neuroma.

I would recommend seeing a podiatrist to get a definitive diagnosis.

I just read the title of your post and realized that the bump is on the heel. I have plantar fasciitis and heel pain but cannot feel or see an actual bump. Sometimes people with plantar fasciitis have a heel spur which often isn't what causes the pain.

At any rate, I still suggest letting a podiatrist diagnose your problem.