Have you checked his tank temperatures, and the temp on his basking site? If his temps are a bit too high, that could be why he's gaping like that. You should be using a digital thermometer with a probe to check his temperatures. If you don't have one, you can pick one up at any Walmart for about $12. Unfortunately, the thermometers that you buy in pet stores are notoriously inaccurate, and sometimes may be off by 20 degrees, either way.
To get an accurate reading of his temperatures, you should place the digital portion of the thermometer on the floor of the cooler side of his tank, and attach the probe to the object that he uses as a basking site on the warmer side of his tank. That way, you're measuring the actual temperature thats up against his tummy after he eats, instead of the air around it. The temperature of the object that he basks on should be between 100 and 110 degrees, and the cooler side of his tank should be between 80 and 90 degrees.
If his temperatures are fine, and he continues to gape like that continually, then you may have to take him back to the vet, as he may have picked up an Upper Respiratory Infection. As I mentioned before, the humidity in his tank could be elevated, due to the waterfall in his tank, which may be causing problems for him in his weakened condition.
Have you noticed his sitting up very straight and gazing up at his lights for long periods of time, or sleeping with his head propped up on the glass, or something else in his tank. Both of those things can also be one of the first symptoms that you'll see if he has picked up an Upper Respiratory Infection, since being in that position will help his sinuses to drain, and make it easier for him to breathe. If he has picked up an URI, that could also be affecting his appetite, and he'll need an antibiotic to clear it up, If you still have the Baytril that the vet prescribed, you might want to check with Tracie to see if she thinks it would be a good idea to give it to him, just in case. She can also advise you on the dosage, if the vet didn't indicate how much to give him.
Another thing that you might want to consider, because of his poor appetite, is purchasing a tube of a product called "JumpStart", which is manufactured by Zilla. It is a concentrated caloric supplement and appetite stimulant for reptiles who are off their food, due to illness, or other reasons, and is chock full of all the vitamins and nutrients that he needs to keep him healthy if he isn't eating well for you. It is sometimes difficult to find in local pet shops, but you can purchase it online at ReptileSupply.com, and the cost is about $10. It comes in a tube, in a molasses based, paste form, and if you mix about a teaspoon of that in with about a half jar of his baby food, he may be more willing to eat for you, since its sweet, and most of them like the taste of it.
If you end up having to give him the Baytril, then you may also want to order a bottle or two of Acidophiliz+ from ReptileSupply.com Acidophiliz+ is a probiotic which should be given to beardies who have taken, or are taking, an antibiotic, since antibiotics will kill off all the good bacteria in his digestive tract, which are what cause him to feel hunger, and also help him to digest his food. Giving him a probiotic, such as the Acidophiliz+, will replace those good bacteria and should improve his appetite.
If you are interested in how it works, and how to provide more supportive care that might improve his appetite. I would recommend that you read through my article "Supportive Care During Antibiotic Treatment for Coccidia and Other Intestinal Parasites". You can find the article by clicking on the "Care Sheets and Articles" link at the top of the home page here on the forum.
Although we don't know for sure that he has parasites, the supportive care would be the same, since, if you have to give him the Baytril, he is taking an antibiotic, just for a different reason.
I will send Tracie a Private Message, and alert her to the fact that you may be having problems with him again, due to his gaping. I'm sure that she'll check here and read this thread, and then can advise you on what she thinks would be best for you to do.