Hi. For The Past Four Days My Stomach Hasn't Been

Hi. For the past four days my stomach hasn't been agreeing with my lately. I've been experiencing a burning sensation that comes and goes along with the feeling to vomit. My appetite is completely gone, but I still try to eat once in a while and drink a good amount of water. So far only apples have gone well with my stomach, and everything else has given me a stomach ache. I've also been experiencing problems when I defecate. So far its come out in liquid form and I've found myself struggling in the process. I then also feel my lower abdomen grumble loudly. Can you give me a guess on what this all might be???