Is it the Flu or has the Reflux/Gerd returned after 7 months of no symptoms?

I have a 18 month old boy and he stopped taking medication at 1 year, all symptoms of acid reflux/ Gerd stopped, he was a perfectly normal healthy little boy. Recently last weekend, he began to throw up and have diarreah, we went to the dr and he said it was simply the seasonal flu, well it has been 6 days and he is still throwing up, usually when he first gets up in the morning is when he vomits and oddly enough its only once, always after he has been laying down tho, and the diarreah will continue throughout the day, no fever and he is very irratable, doesn't want to be on his back again to get diaper changes... I fear that his reflux is returning and that this is more than just the seasonal flu. If it was flu wouldn't he be throwing up every time he ate throughout the day rather than first thing in the morning or after naps after the food has sat on his tummy? I'm one very conscerned mother and I just want to know if anyone out there has been through this?