I quit smoking and now i have canker sores, how do i get rid of them?

been smoking since i was 12. i quit multiple times but to the same result, horrible canker sores on my gums, lips, tongue. i dont know what to do. lat time i quit i did for 6 months and had them the whole time. they are back now worse than ever, i have over 21 of them! i need help. i want to quit but not if it means living in excrutiating pain for the rest of my life....