Concerned about my son's abdominal area

[Loveleyangrl]

So my son who will be 13 on the 27th of this month who by the way is very healthy and physically active on the regular. But began suddenly experiencing some pains in his mid and left stomach while playing on the trampoline like normal, then when coming inside to eat dinner became nauseous and got sick a little. So being an experienced CNA my first reaction was to lay him down on his back have him relax and do a standard belly check. Placing my first finger at his sternum I got 3 fingers down when not only did he say hurt very bad but so discovered a small knot, then in checking both sides by the ribcage areea up and all the way down and over both sides from of his chest/stomach . His pains are only from the sternum down right at his belly button crossing over along his left side. He was unable to eat the pizza from dinner but able about 29 minutes or so after to eat some non acidic fruits and water, so my first concern is leading between gurd most mild, gallbladder or an ulcer. It was very late in the evening so I left a message for his pediatrician and while waiting for a call back in the morning decided to do some research.