Probiotics, good multivitamin/mineral, and lots of small high-protein snacks and meals. I have little/no appetite or hunger, even worse little thirst, and I have to force myself to eat & take beverages by the clock - something every hour. When I first had MAC,began losing weight & it accelerated with antibiotics (on them for a year now) until I was down 20 lb - which I didn't have to spare.
Now refrig is stocked with high-calorie cheeses, full-fat dairy products, protein bars and juice (never used to drink it - just water & coffee.) I put extra protein powder and milk or cream in smoothies, soup, chili, oatmeal... Never skip a meal even if I only manage a small portion. Instant breakfast & cream in my morning coffee. Many of these suggestions came from a friend constantly battling to maintain her weight because she cannot eat solid food. With this I have managed to just about maintain, even though I am now taking the antibiotics daily, and feeling very tired because of it. I think with the antibiotics disturbing the flora in the gut, there is also lack of absorption of nutrients, which makes the problem even worse.
If you feel you have slipped into anorexia, an true aversion to food/eating, some counselling may help.