HI, My Daughter Takes Naproxen For Her JIA Condition And

HI, my daughter takes Naproxen for her JIA condition and has been having chest pains, I believe from Naproxen. I called the doctor and told him about it and he said to give her Omeprazole first and then other medicines. I gave her Omeprazole and now her stomach has been hurting all day. Is this a common symptom in the beginning and when does it go away? she is also constipated and is having a hard time passing a stool. What do i do? Thank you.