Hello Mam, There are various types of ulcers and where different type of ulcers require a different type of treatment, first note the on set of unlcer, whether it's painful or it comes and goes often or it been there for long time, if it comes occasionally then it might be due to vitamin deficiency, it it doesn't go for a longer time or you notice any near by tooth with sharp margin then you have to get your consult done with your dentist.

Ulcers can occur due to various causes. So please have it investigated properly. But becosules which are multivitamins might help if there is any underlying deficiency. It’s usual dose is once a day but can be taken twice a day if confirmed deficiency.

Once a day should be fine. Take for 2-3 weeks at least