Getting sick when traveling is absolutely more common, you're exposed to foods, diseases, weather, and people that you aren't used to. However if it's happening reliably and specifically after flying as opposed to other forms of travel that does sound like it could be a specific problem. It could be an inner-ear thing since airplane compression can fuck with that
It's not a perfect solution but sometimes when I fly I wear a mask to reduce the odds of getting sick, though it's pretty rare I get sick from travel myself, and I travel internationally annually