The blood blisters mainly occur due to trauma or friction and they resolve on its own. Please check for the tooth that is causing the friction or the trauma from cheek bitting.
Next Steps
Visit the Dentist and find out the actual cause and treat it .
Health Tips
The reason for blister other than above mentioned might be due to
1. Hot and spicy foods that irritate
2. Allergic to any food ingredients
3. Due to chemotherapy ( medication you are using for your other medical issues)
4. Thrombocytopenia ( please get a platelet count done to rule out this conditions)
Hope this helps you...