Seems like I a weird thing to ask but I'm in a bad spot. What are some foods that are high in calories, but low in fats and sugar?

I'm struggling right now to even get a third of my recommended calories. I keep loosing weight and I can't loose more. Its really interrupting my life. I am having a really hard time even getting a third if the calories, it just seems like sooooo much food. I have little to no appetite at the moment and my bf is really getting on my case about this. And he's right, I just don't know how to get more in right now.

I'm having gallbladder problems so I don't want much fats, I also cannot have lactose, casein, or gluten. I'm at a loss. I eat some meat, not nearly enough and I only eat white fish or chicken breast. But chicken breast is soo expensive, I can't really afford it. I am on disability so my food budget is tight.

Any ideas would be appreciated .... Thank you!