Having Stomach Pain. Feels Sleepy And Vomiting. What Should I Do?

My two year old gets stomach aches frequently. Almost every few days she will tell me her tummy hurts and she can pin point it. Along with the stomach ache she acts really sleepy. She will come home from daycare and want to lay down on the couch with no dinner. At first I thought it was just a stomach bug. A couple of times she has thown up. I get worried because when she was younger she had an IGG defieciency in the pneumonia antibody. She has always been small forher age so they did a digestion test on her, and realized she digests slower than normal. What should I do