Jalpari…your body is not invincible. It is also susceptible to wear and tear. You have to treat it well. If you are underweight already and all are you consuming is liquids…how long do you think you will be able to work out and be healthy? 
Incorporate meat into your diet and light carbs in the morning. You have to get your body used to healthy eating habits varna kya hoga ke when you actually start to eat human food you will blow up like balloon.