Hi Sleevefox, this is a bit unusual but it sounds like your body is just adjusting to your new condition. Mention it to your physician on your next visit though. It will take your body a while to adjust to your new stomach size and a lot of interesting things happen during this process. You will adjust and learn what works and doesn't work for you.
I suggest that you keep a little journal of your food intake to reflect what you are eating and drinking, the quantity, the time of day and the reaction. It's helpful to you and your physician to determine your progress and how your body is responding. For example, I learned that I can no longer tolerate any carbonated beverages or eat anything within 1 hour of bedtime. This often resulted in gagging or vomiting, sometimes while I was sleeping.
The first three months following surgery were the most challenging for me. I worried that I would never eat more than two teaspoons of food and wouldn't get the necessary Protein and nutrients. I thought that I had made a huge, irreparable mistake. Once I figured out what my body needed and how my new stomach worked it went very smoothly. It's been a year now, I've lost 50 lbs. and am eating small adult portions. I dine out with friends and they have no idea that I had the surgery, they just think that I'm being good with my diet. I have not felt this healthy and vibrant since I was a teenager, over 40 years ago. Best decision ever.
Good luck.