I am getting more and more ill, every time I eat I get agonising stomach pains..?

also I have had diarrhoea for over 8 weeks. I have had a stool sample and blood test done for anaemia, my liver and kidneys and coeliac. They have all come back negative except coeliac which has still not come back! I asked the doctor for something for the diarrhoea and she gave me a pill which worked but gave me the most painful constipation, my stools are now fairly loose but thankfully not diarrhoea (yet) but my colon is so painful I am scared it could be damaged. It was agony. My symptoms are muscle wastage, weight loss, diarrhoea, severe abdominal cramps, occasional nausea, malnutrition and this has all made me very 'low' and emotional. I am only 15, last year I had major spinal surgery in June for scoliosis but I was strong and recovered well. I cry practically every night for stupid reasons- one time it was because I sat down to a meal and it wasn't what I wanted. I have also been craving food like kfc popcorn chicken, McDonald's happy meal, nachos, haribo, I don't have that stuff very much and it's weird that it's all so unhealthy. I am just getting so worried now, it's also stressful at school and when I am upset I keep thinking 'why me? I have already gone through more hardship than most adults last year and now this?!' I am going on a school trip to China in a bit over a month and I really hope I am well enough to go, I don't know what I am asking- maybe someone has seen this before? I know it looks like I am a coeliac but if I am I don't know what I will do- my favourite cereal that I have eaten longer than I can remember is called 'weatabix' for crying out loud! It just seems so unfair, I never used to be ill and now it's just been non-stop bad illnesses.