Child With Mouth Ulcer. Given Antibiotics. Not Having Food Properly. Getting Bleeding Some Times

Hi there, I have a 13 month old baby, who recently stopped drinking his formula, refused his dummy, didint want to eat or drink anything. Upon closer examination, i realized that he had mouth sore. I took him to the doctor who advised that it was a viral infection & mouth ulcers . he gave him an injection , antibiotics & mouth ulcer medication . its now the 8th day & he seems to be fine, eating & drinking water, but still refuses any form of bottled/sippy cup milk & his dummy completely. the Doctor also told me that he has a problem with his mouth where his upper lip is attached to his teeth in a way that s going to affect him later on in terms of speech. I thinks its called his frenulum. Its causing a seperation of his 2 front teeth & that also looks sore & infected up until today. Doctor advised to have an op & slit it, as soon as possible. Please can i have some advise on this. Should i do it, as I noticed that it bleeds sometimes & there are still mouth sores on the centre as i cant completely pick up his upper lip to check due to this frenulum being attached on the teeth. I m so worried. Please let me know if i need to go do the op, or will he grow out of it. thanks so much.