I had an excisional biopsy about a month ago on my foot, whenever the area on my foot even slightly touches another surface, it causes a lot of pain. is that normal?

No: This actually happened to me. Clearly one of the nerves in the foot has been effected and it could just be that the nerve is being compressed by post-operative inflammation and scar tissue build up. You need to talk to your surgeon. Most of the time, this goes away. The most common cause regardless of surgery: a neuroma: https://mayocl.in/3g27FtW