I am getting aphthous ulcers after almost quiting smoking. what should i do?

Quit entirely.: There are so many changes going on within the cells that are exposed to smoking that it is often hard to predict what is causing what, or if there is only a temporal relationship, and not a causative association. Quit smoking entirely. And use whatever help or means you can to accomplish it. The most important step, and the one that will probably making quitting successful is the decision to quit.