It is difficult to tell from what you described whether this is a case of sinusitis and/or tonsillitis. It is possible to have a sinus infection and have all the symptoms you described. These can be chronic in nature or even come and go away. The best way to make a diagnosis of sinusitis is with a sinus x-ray or CT scan.
It sounds like the Mono in November also changed the way your tonsils are functioning. It is possible that you have been harboring an infection in your tonsils, which could also give you the same type of symptoms. It is an excellent idea to have an Ear, Nose, and Throat (ENT) specialist evaluate the problem and get to the source.
Good luck
Any feedback would be appreciated.
jo