Any ideas why 5mo is throwing up at night?

Hey all. So I have a 5 month old child. He is 100% happy and healthy most of the time, however the past few days he has been vomiting in the middle of the night. Saturday night he vomited twice at night (around midnight) and nothing Sunday, but then again just did it now (Monday night at about 11). He is eating fine, peeing, pooping, doesn't have a fever, etc. And it 100% is more than spit up and occurs maybe 2 hours or so after his last feeding.We didnt change anything in his routine. And he is still on strictly breastmilk so neither his nor my wife's diet changed. We are at a loss as to what could be causing it. Thoughts? via /r/Parenting http://bit.ly/2Tk8JOb