Hello and welcome to HCM,
After reading your history i would add few possibilities , first of all Apthous ulcers are the most common ulcers seen with exact cause unknown they may be caused by physical trauma,chemical injuries like citrus, vitamin b deficiency
, stress related , immunodeficiency
disorders , food habits ,tobacco and alcohol addiction and so on..
they are painful with rupture of mucosa and if secondarily infected with herpes
or bacteria needs antibiotic coverage to treat.
In your case ,since you are a tobacco user i would suggest you to get the lesion diagnosed by a oral surgeon before predicting it as apthous .
apthous ulcers take 15 to 30 days to resolve depending on your body immunity so u can wait for some time.
you can continue with antioxidants LYcopene2000mcg od, vitamin C
lozenges and vitamin b supplements BID , tetracycline
tablets BID for 7 days , use antiseptic mouth wash for oral rinsing .
get well soon ,