It sounds like you have lost your appetite or else you are not absorbing well. You could have vitamin and mineral deficiencies.
When I had malnutrition because gallbladder stones made me nauseated and robbed me of my appetite, this was how I was thinking - what's the formula for putting on weight? I had no drive to eat, but I felt like I was caving in all the time. I was anemic and low in vitamin D. Turned out I also had Celiac disease causing malnutrition.
Your profile says you are a woman, but you are posting under men's health.
I'm not a women I just made a quick account
You have to eat at regular interval of 3 hour. start with light food then move slightly to heavy.