I've had crampy feelings above my navel for3 MONTHS but no pain at night and a bit of lower back ache iam a blood donor and they take my blood ok thank?

Need closer eval. I am not sure what you have available to you in the UK but need to see your doctor. The area that you talk about could be the small bowel or any of several organs. See the doctor as a intrabdominal issue could explain the problem. the blood donation is a non issue.