These may be aphthous ulcers. "Aphthous ulcers are also known as canker sores. They are painful, temporary sores that may occur anywhere in the mouth, although less likely on the gums, lips, or roof of the mouth. They can occur one at a time or as a group of sores. Although these sores are not serious, other mouth sores may be."
There are several factors that have been associated with aphthous ulcers: viral infections, vitamin and nutrient deficiencies, food allergies and stress may lead to aphthous ulcers. These may be extremely painful and may recur .There are bigger ones which may be greater than 1 centimeter in size and may be extremely tender.
The underlying causes should be ascertained. Vitamin supplements may be given and supportive therapy such as increase in fluid intake, a lot of rest and antiviral medications may help. Corticosteroids have been used in treating the severe forms.
Discuss this with your physician and avoid biting or picking on the lesions as this may only aggravate the condition.