Normal but awful when you’re going through it.
DS first year at nursery was an endless horrific routine of bacterial tonsillitis, chest infections, ear infections and then we’d start the cycle again. Sometimes with a HFM, croup or norovirus thrown in for lols.
Went on for a year. Went to a&e with him I think 7 or 8 times?! (fevers over 40 not responding to antipyretic, retractions when breathing, petechial rashes...) it was fucking horrific. He was so ill. And miserable. I lost an incredible amount of weight with the worry. I’m a single parent so was barely sleeping then working all day... god it was desperate.
In the end, I paid for a private paediatrician to run bloods (GPs advice as waiting times super long on NHS) to check for autoimmune issues. Nothing to see. Private doc said one more bout of tonsillitis and we’d do broad spectrum long term antibiotics and book a tonsillectomy.
So with that hanging over us, when he had his first christmas holidays a few weeks after, by which point I was on my knees and he looked like a Victorian workhouse kid- all blue under the eyes and sickly pale- I basically banned all family visits, bought really good quality vitamins for him and me, set a strict routine of breastfeeding, walks in the fresh air and naps, and early nights, and did it for 3 weeks religiously. Like a sort of at home sanatorium 
I don’t know what it was - maybe coincidence, maybe the rest?- or the break from nursery to let his immune system just take a breather?- but something worked. seemed to break the cycle of illness and after that he was fine. Never went to a&e again- oh actually just once, for acute croup, and once for a nasty fall and head bump.
Not suggesting you do the same, but just to say.... been there. We survived and you will too
DS now a thriving 5 year old- asthmatic, but very well.