I've been struggling with this too

but I've decided to accept my skinny body coz gaining weight is nice but losing it can be so depressing
What I did to gain almost 10kg >
Drinking a protein shake twice a day (morning and night)
Drink 10 cups of water a day
30 minutes of sit ups and squats
Go for a jog atleast 3 times a week
Eat bigger proportions
Eat more potatoes in your diet
Eat a large meal after 8pm
Snack on bananas as much as you can
I gained so much weight , a lot of it went to my ass

and then I lost it all 2 months later when I got lazy