Nice to see your posting. If this was done 3 years ago, I am not of the opinion that it is the loop diathermy that is the cause of this as the procedure was done a long time ago except of course you mean that it has been red till then, but even then, i do not think we would accuse the procedure to begin with. I think your cervix should be reexamined so as to determine if it is tender/painful and also cervical cancer screening
to be done: Benign hyperplasia
) or beginning of cervical malignancy could be responsible for the redness. The redness could still be normal, as we do not know the state of your cervix prior to you visiting the doctor.
In any case, I'll suggest you visit your doctor for a closer examination and testing.
Wish you the best