When I was young, I had a severe case of it. For two weeks I had a 104 fever that spiked and crashed and was very sick. I went back to college (it was Xmas) and they did a mono test and I was very positive. Then the sore throat came, after the fever stopped, and they put me off saying it was common and viral.
Well, it was STAPH and I finally made them culture it. Seems that the virus weakens you and you get opportunistic infections any time during the course.

My son's mono 4 yrs ago was much milder. He did not have the fever, but after about 2 weeks of feeling terrible, his throat swelled up. It was May and he had
just come home for the summer, so I sent him to my doctor. She thought mono right away, and did a mono spot...but his throat was a mess. No strep or staph in it but she gave him Amoxicillin and that knocked it out. He was really tired for the whole summer and part of the fall, however.

Mono is very debilitating.

And any severe infection will throw off the blood work for a while.
If you have EBV/mono, your liver functions may go crazy. My son's were terrible for over 6mos, and he had to cancel plans for the wisdom tooth extraction he was planning. Doctor wouldn't let him do it.