welcome to healthcare magic forum,
             As said by you that u r recovering from 
bronchitis, it means u would have had a many medicines, so ur 
canker sores could be due to those medicines commonly known as drug induced 
gastritis. also many other reasons for canker sores which u must rule out is 
Constipation, Reduced quantity of water intake, Lack of proper sleep, Stress, long standing illness, Acidity?
          As u r out of country advised u to get an 
antacid and start it of daily before meals once a day. along with this have a proper meal which should be properly seasoned and not pungent, have proper sleep and make ur sure u have regular bowel evacuations. and relax. if u can get homoeopathic medicine then suggest u to take Borax 30 two times a day for 5 days. along with this also u can apply (paint) glycerine on inside of ur mouth 2-3 times a day to relieve u of ur pain.
   for further queries contact aashirwadhomoeopathyclinic@gmail.com
take care.
Regards,
Dr. Rooma Ramnani