Sick kid

How do you handle it moms? I hate not knowing how my kid got sick and with what? I hate not being able to make her feel better. I hate that she’s at the age (3.5) and refusing everything so then she just remains more miserable for longer (won’t let me suck her boogers, she’s not effective at blowing it out, won’t take liquid medicine only chewable). I’m starting to learn she vomits every time she’s congested but this time is the worst and I don’t know what’s going on. No fever thank goodness so we just have to wait it out for a couple more days. I’ll take her in if she gets worse. Why do kids get sick so often? Anyone have good tips or tricks? Good medicine or preventative? We were taking vitamins and trying to practice good hand hygiene.