I've been eating like crazy since takedown. First few months are rough I'll agree to it. There's a lot of learning curve, some foods will agree very well with you, others might not. I was down to 42 kgs post takedown but now at 60 kgs and fairly lean mass. The key is to eat alot of those right foods. I eat many brown bread slices with peanut butter spread or regular butter. Chicken cooked in olive oil also help me put on mass. Rest boiled sweet potatoes, bananas , hard boiled eggs are something I eat regularly.
I workout almost daily so thats also helped me in increasing my body's ability to digest well. You need to get out that phobia of not eating enough if you want to put some mass.
Try doing Intermittent fasting , there's a lot of information about it online.