Talk to General Physician on Can't Gain Weight

I’m a 23-year-old, 5′4″ tall, and my weight has been around 39–42 kg. I’ve struggled to gain weight for a long time. I usually eat two meals a day because I don’t feel hungry enough to eat more. My blood tests from April showed: - Ferritin: 12.8 ng/mL - Vitamin B12: 242 pg/mL - MCV: 82 fL - MCH: 26 pg - RDW-CV: 16% I’m taking a B12 supplement. I started iron tablets earlier but couldn’t take them consistently because they were large. I’m starting iron again today. I often feel tired, and my blood pressure tends to be on the lower side. I’ve tried both Trimetabol and Apizyt syrups, with little effect. With Apizyt, I noticed a slight increase in appetite for a few days after finishing the bottle, but not much while taking it. I’ve also tried Ensure, but it’s too expensive for me to use regularly. I don’t take any other medicines. What could be causing my low appetite and difficulty gaining weight? What should I get checked? Is there an effective appetite treatment that won’t make me sleepy during the day, since I’m already tired and tend to have lower blood pressure?