What to do if i have extremely painful canker sore..how do i heal it or at least make it feel better?

Keep it clean: Clean the area to prevent bacterial superinfection. Palliative treatment would be orabase, orajel, over the counter numbing gel, chloraseptic spray... The topical spray works well if you dried the area with gauze prior to application. 3-5 days healing time is normal without any medicine intervention. In the extreme severe case, antiviral (acyclovir) and/or laser treatment recommended.