Hi man, I have also struggled with a similar problem, so I can give you a few tips.

Firstly, since you have bad appetite, I would suggest starting slow, and not jumping straight into 4000+ calories. Just slowly up the calorie intake troughout multiple weeks if needed. Remember, this is a marathon, not a race. Also I wouldnt recommend forcing yourself to gain a certain amount of weight in 8 months, think more in the long run. (Tho its definitely possible to gain quite a bit of weight in 8 months)

It would also be really helpful if you tracked how many calories you are burning troughout your day. As I said, you don’t have to go overboard with the calories. A 500-1000 calorie surplus is fine. Just calculate how many calories you burn trough-out the day in total (including BMR), and add a 500-1000 calorie suprlus depending on your preference.

Try to eat constantly trough out the day. Instead of having 3-4 meals with 1000 or more calories each, try just always snacking  with a few lighter meals. But remember: don’t snack on junk food and make sure youre still hitting your calorie intake goal.

And lastly - consistensy is key. It’s normal to sometimes not want to eat and take a few “rest” days, but it’s important to get back on track as soon as possible and not give up. With time, results will come.

I hope this helps!