Hello,
Thank you for you query at DoctorSpring.com
I understand your concern.
Cold sores have different etiologies, such as stress, diabetes, repeated exposure to Herpes Simplex Virus, Vitamin deficiencies.
In regards to your immunity, diabetes can further compromise the immune system and predispose you to getting frequent outbreaks.
I would have to agree with your Doctor's opinion and I feel you should get your sugar levels checked as well as a complete blood count, which would help in diagnosing an infection or iron deficiency anemia.
Kindly do get the tests done, and you can share it once you get the reports.
Regards,
Dr.Jay