Why Do I Always Feel “Tension” After Eating Anything?

I've been trying to exercise more and more frequently(small win for me but today I did a 4.5 mile run!), but for some odd reason, not matter the amount how little, or what I eat, after dinner, I always feel some "tension" in my stomach like I've miraculously gotten gained a good amount of belly fat over the course of 20 minutes or so. Does anyone else experience something similar, and why do it happen?