To gain weight

Hi. I just went for my 2nd checkup today. My weight from 65kg and now currently 62kg. So i loss 3kg for a month. And now another 2 weeks I have to go to clinic since doctor said it is not okay to lose so much weight. ?? i just can eat dry crackers and milo only. Other than that I will vomit back. Any ideas or maybe suggestion I could try? Doctor ask me to take multivitamins, but I can’t even take any pills now!??????????? but my baby is normal and healthy, ?? ?