toddler not eating

My toddler is not eating, he is a picky picky piiicckkkyyy eater 19 months and weights 22 lbs I feel like he too skinny lol shoot my newborn is month in half and weights 12 lbs lol.. 
My question, are toddlers normally loose appetite? I have tried everything and he is rarely hungry or just doesn't like it depending on how he is feeling. It's frustrating because he may like one thing right now and the following day he doesn't want it. Or simply won't eat. Need advice lol