constant illness after mono?

my son was diagnosed with mono early January ended up hospitalized with a throat abscess and critically low blood platelets (got transfusions ) has been out of the hospital for about a month and is just getting constant illnesses- respiratory infection, followed by a sinus infection. constant coughing and headaches. He made it to school every day this week for the first time since december and now has fever and chills. (we will test for the flu later.)

he’s taking all kinds of supplements, washing hands often, showering after school. is this normal? he’s a senior so luckily his schedule is easy but this is crazy