I'm sorry you are going through this. I had nausea and a feeling of fullness after my surgery as well. Between chemo and my surgery, I lost more than half my body weight. Please indulge a few suggestions about the nausea before I let you know what I tried to help with eating.
Re nausea:
Are you on any antibiotics? Because these can cause nausea and were part of my problem. In fact, check the side effects of any new meds.
Have they checked your blood work, especially metabolites? That was also contributing to my problems. And given you have an ileostomy, I think you are prone to electrolyte imbalance.
Re: eating
If there is nothing more to be done about the nausea, it may help you to develop a strategic approach to eating.
Make every bite count, which means maximizing calories and protein in every bite.
Prioritize protein. It is essential for healing, and you will need that during chemo. Perhaps try high-calorie, high-protein food supplements like Ensure. I found it easier to force down a big gulp and wait a while before the next big gulp. Some people may be able to take small sips over time, though it didn't work for me.
I found it easier to drink than to eat; I did a lot of broth!
Try easily digested things like rice and pasta. I found a small portion of rice very settling to my stomach, and it would sometimes help me eat a little more. A dietitian suggested I add butter to the rice for extra calories. I frequently added gravy as well.
Try smoothies in any flavor you like. The dietitian suggested adding peanut butter to boost calories.
Try sucking on hard candies.
FYI, being overly hungry for a long period can, itself, make you feel sick. Getting any kind of calories in your system may ease the nausea a little (won't fix it).
If you are continuing to lose weight rapidly, talk to your provider to see if they can give you some IV nutritional support.