hello and welcome to HCM,
You may be right in assuming that you have tonsillitis
while infectious mononucleosis
is more of a lab diagnosis and you cannot make that by comparing pictures!
As regards to the opening, it may be that an abscess
pocket has formed within the tonsil or even that the crypt may have deepened.
In any case you need to consult your ENT doctor so that he can properly examine the tonsil and give you a proper treatment for the same.
You may even consider throat swab for culture to get a proper diagnosis
You may even consider injectable if the pain is severe
take only warm fluids and avoid anything spicy
Dr Sriram Nathan