Just looked up on babynet
There are different types of ulcers depending on whether they are caused by viruses or allergies, but the most common are aphthous stomatitis – small, white, uncontagious sores also known as canker sores or aphthous ulcers. The cause of aphthous stomatitis aren’t known, but it’s thought that insufficient sleep, insufficient intake of nutrients, fatigue and a drop in immunity levels can cause an overall worsening of one’s physical condition and cause aphthous stomatitis to appear.
The baby in you uses up the nutrients in your body, and this can deplete the reserve of nutrients in you and cause aphthous ulcers to form. This is especially so in the first trimester of pregnancy when the hormone levels change and ulcers form on your tongue or on the insides of your mouth more easily than usual.
Basically Sarah just needs to eat some fruit and veg!