Get yourself a box of Tension Tamer tea. It is by Celestial Seasonings and tastes a TON better than chamomile and it is more relaxing than straight chamomile. If chamomile helps, typical teen will likely help more. I swear by it. It is at most grocery stores and Walmarts.
I am SO SORRY that your son is going through this. I think it is criminal that they have not given him pain medications. I would have a FIT if they did that to my kid. I think that is sheer cruelty to make someone recover from major surgery with-o pain medications. I sure would not be eating if I didn't have pain medications after surgery. Even the thought would be scary.
I would suggest beef or chicken broth for him. It can help settle his stomach. I know my mom would suggest baby beef or chicken as they are easy to swallow and have protein and are not sweet. Personally they make me sick, but it is a texture thing as that is my major sensitivity. It might be something he could choke down to get some nutrition.
I hope and pray this isn't cancer. That would be my biggest fear also. Please contact his doctor and let them know he is in a HUGE amount of pain and is not able to handle school yet, esp without pain medications. Tell them flat out that tylenol and ibuprofen are not cutting it and that he NEEDS appropriate pain management. I think it is sadistic to make him go through major surgery liek this with-o pain medication. I think you should have an absolute mother lion eating the idiots moment as you chew them out and ask if they wnat you to perform surgery on them with-o anesthetic and with-o pain medications after = if not then they NEED to manage your son's pain appropriately. You also need to coach him to tell the doctor how it hurts terribly and to show the pain and not hide it. They will try to brush you off but as his mom you need to advocate for him. As a patient he has the absolute RIGHT to appropriate pain management!!!
This tool helps rate how much pain you have with different tasks. It may help you explain to the doctor how much pain your son is in. https://theacpa.org/uploads/documents/ACPA-AbilityChart.pdf
I would look at various drinks to get him to drink liquids rather than pushing food right now. Chances are that food may hurt as it moves through his system. Pain can make you very nauseous and it may be a problem with keeping food down. I have that as a major issue and sometimes food can even trigger the nausea once it is in my stomach, esp if I am in a lot of pain. Water often upsets my stomach, esp tap water. I hope that you find something that he can eat soon, and drink.
(((((hugs))))) I am so sorry that your son is going through this, and that you are having to deal with the increased anxiety on top of your regular anxiety issues. You are all in my prayers.