welcome to Health care magic.
1.If the pain is severe then you can take 
morphine which is prescribed ( but not recommended on a regular basis )
2.With a chronic 
irritable bowel syndrome you need to take a good care of your diet. Rich finer diet, plenty of fluids (avoid constipations), avoid junk, spicy and fatty food. 
Probiotic yogurts available in the markets (you can try).
3.The loos of weight and appetite - should be evaluated.
4.In this case i you are my patient after examination, i would recommend you to get a CECT abdomen ( contrast enhanced computer 
tomography ) Helps in exact diagnosis of the bowel pathology and presence of any mass lesions.
5.So see your doctor and get the needful things done.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.