Toddler sickness bug

Can you catch a sickness bug without being sick? My son has been doing a cough/gag for a few days and is quieter than normal. He’s barely eating but otherwise seems pretty fine in himself. I’m driving myself nuts trying to work out what’s wrong with him as he definitely isn’t 100% himself but isn’t showing typical poorly symptoms! He will brush his teeth at night but not in the morning (pulls a face and does the cough that looks like he might vom) and will only eat certain crisps and sometimes a yoghurt but even that made him gag this morning. It’s been going on for almost 3 days now but he hasn’t been sick! Also does the cough more at night as he’s gone to bed then settles into decent sleep around 9.30pm and in the morning for the first couple of hours of being up and about.