URGENT! MOUTH ULCERS AND TONGUES ULCER?

i having chicken pox since a week ago. now i few mouth ulcers in my mouth 4-5. all of these ulcers do not pain anymore. but just not yet heal. and the ulcer at tongue quite big, diameter around 1 cm. are these common? can explain? how long should this ulcers take to heal normally? these ulcers had around 1 week already. thanks