Painful sores on roof of mouth, like semifirm blisters cant really see them. spread to gum across palate. also palette slightly numb as if scalded.

Roof of mouth sores: May be a viral infection, a result of trauma, an allergic reaction, from acid reflux, a side effect of a systemic disease. It is impossible to diagnose accurately without additional information and a clinical and visual examination. See your dentist, an oral surgeon, or an ENT specialist for an examination.

Canker sores: is the most common oral lesions. Most tongue ulcers, infections will clear up by themselves within a week or two. You should see your GP or dentist if the ulcer gets worse or lasts for longer than 2 weeks. Oral cancer appears as a growth or sore in the mouth that does not go away. If concerned see your dentist ASAP.

Multiple Causes: Hard to determine without visualization and discussion. Could be an allergy or even a thermal burn. Please see a local dentist of the problem has not resolved in a week or so.