My boyfriend has white exudate on his throat and was told that it wasnt strep throat what else could it be?

Several ideas: Any viral tonsillitis such as adenovirus or mononucleosis can cause exudate. A strep culture or rapid strep only looks for this bacteria. Other bacteria such as hemophilus can be identified by routine culture methods. Suggest getting mono spot blood testing and routine culture if the exudate and other symptoms continue.

Might be mono.: Mononcleosis can produce an exudative pharyngitis that can look for all the world like a strep throat. There's a blood test for mono. I have seen people who have had both mono and strep at the same time. Clearly, the strep needs to be treated with antibiotics - or it can produce heart valve or kidney damage later on. Mono runs its course, though sometimes medications are used to control symptoms.

Any other germ: The throat & tonsilar glands are the primary entry point for all germs that enter the body. Skin surfaces serve as a good barrier otherwise. The treatable causes of throat exudates include strep A and Diphtheria. I assume he had this shots & boosters & does not have this easily recognized disease. Primary mono will last 3 weeks or more, lesser germs will fade quicker without treatment.