I am currently having the same problem. I haven't told anyone yet, because I am scared. Let me know if you find out any answers.
Hi,
The cause for your symptoms could be a sinus infection .It could have been aggravated by a dental infection . Since sometimes the roots of teeth are very close or inside the sinus , periapical infection of the tooth may cause pus formation in the sinus . If the pus doesn’t come out through the tooth canals , it is likely that discharge will be through the nose . Please consult your dentist and ENT surgeon for examination and diagnosis. Hope this helps you . Take care and regards !