It takes a while to get your appetite used to having a larger intake. I used to live on one meal of a few chicken tenders at lunch and a sandwich at night.
It is absolutely possible to live on that few calories, I've been there. However, you need to start giving your body the nutrients it needs in order to build muscle.
I was at ~1200-1500 kcals and I have a super fast metabolism, so that was absolutely nothing. However, made it my goal to hit 2000 kcals every day. (sometimes with protein shakes, sometimes with bars, sometimes with Orange juice and cake. Just any way you can, set yourself up for a calory goal).
Later that went up to 2500, then 3000, now I'm eating ~3000-3500 kcals/day and I could easily down 5000 (my cheat days easily go over 5000 and I'm not even trying). However, once you get your appetite working and you are eating a lot more than you used to, try to eat clean and count macros. It makes no sense to clean up your diet if you're downing 1500 kcals/day. Since you're not eating enough to gain mass. Get your body used to more and more food every day just like you would progressively overload your muscles, but do it with your digestive system.
Also know that liquid calories are the BEST way to up your calories without feeling super bloated all day because they fill you up for only a little bit of time.