Does Hormonal Imbalance Cause Stomach Ache And Appetite Loss In A Child?

Hi there, I have a question about my 10 year old son. He is normally very active and happy go lucky and goofy. Always trying to make people laugh. Recently he has seemed different. Stomach hurts, no appetite, biting his lip like he is nervous but he says that he doesn t feel nervous, but sleeping is off. I m worried about him maybe having vitamin issues, but then I wonder if this could be hormones? My older son seemed more nervous around this age, (he is 13) and has calmed down in the past year...but i m worried because this is not like how my younger son usually is.