My mom has blisters inside her mouth she saw a doctor but doesn't find anything wrong nor get any medicine for them what can she take for the pain?

Oral blisters: Blisters can be painful, topical oral analgesics and tylenol (acetaminophen) or nsaids if no contraindicated will be helpful.

Canker sores?: It would be good to know what the condition is, but if the doctor thinks it isn't serious it's likely to be canker sores, gels for baby teething pain is good to use or you could try clove powder or a clove extract, applied directly to the sore area.