My canker sore in the lower part of my mouth has not healed and it's been over a month. it stopped hurting after the first few days. ?

Canker sore: Get to a dentist and have this area checked. Since it has not healed in a month this my not be a common canker sore.

See Oral Surgeon: Since it has been 1 month, it may not be just a canker sore , but something of more concern. See the Oral Surgeon as he/she would be the treatment provider if further diagnosis, biopsy, etc. is required. Go soon. Good Luck.