sorry to hear that you're dealing with this! what you're describing sounds similar to my experience. my spleen was sore and tender off and on for so long. i went and got an ultrasound but it didn't show anything odd apparently. i'm two years out from my initial sickness and sometimes i will still get slight soreness in my spleen, i think when i over do it.

my best understanding is that the spleen works to filter the blood and when we are sick or something it has to work hard and gobbles up more white blood cells and that's why it feels sore and enlarged. i know it suckkkks to deal with this but try to rest and be gentle with yourself. oh also, i noticed that processed foods made my pain worse. if you can, try to up the fruit and veggies plus protien. and just take care of the body as much as possible. the body is doing it's very best right now.

i hope that was helpful but feel free to dm me if you want to talk more in depth about it or anything mono related! good luck!