Girls, I'm really worried. Today at my appointment, instead of gaining…

Girls, I'm really worried. Today at my appointment, instead of gaining weight, I lost 0.8 kg. I've been limiting myself quite a bit in food because my gastritis has flared up, but I still eat before bed. Has anyone experienced this? And I gained a little weight over these weeks. I'm happy with every kg, and then it's the opposite. Is this even something? On the internet they only write about weight loss when you gain weight, but not the other way around.