1.5 year old getting over viral infection.. super irritable

My son had a fever and runny nose with an occasional cough most of the week. Yesterday when he woke up his fever was gone, today his nose seems a lot less runny... but he is super irritable, having meltdowns over everything, it sucks cause I was hoping once his fever went away he would start feeling better.. but he doesn’t seem to be sleeping that soundly so I’m assuming part of the irritability has to do with him being tired.. my 4 yo was being a bit loud today and woke him up from his nap and I literally haven’t been able to anything since without him whining and crying, he just wants me to hold him:(

Is it normal for toddlers to still be this tired /irritable after being sick or should I be worried something else is wrong?