Welcome to HealthcareMagic forum
Yes, it can be a Streptococcal infection; most of the oral cavity and nasal infections are caused by these organisms. The drainage
from the back of the throat is from the infected sinus carrying all the bacteria into the throat. Due to this, there will be inflammation in the throat giving rise to cobblestone appearance of the pharyngeal wall, these are nothing but the hypertrophied lymphoid follicles.
I would suggest you to drink plenty of warm water, use saline nasal spray
and do steam inhalation 3-4 times a day. You will also require antibiotics which will take care of both sinus infection
and the throat pain.