Sacroilitis can occur as a part of various conditions. Foremost in consideration would be seronegative spond-arthritis. It is a condition which generally occurs in young males but can affect females too. There may be a family history of young individuals with backache or arthritis involving joints below the waist. There may be associated skin or bowel problems. A genetic marker-HLA B27 may be present in many patients. Other possible conditions include infection of the sacroiliac joint by tuberculosis or brucellosis. These conditions are generally accompanied by low fever and a raised ESR. Tuberculosis is likely to be associated with a positive mantoux test. It's important to first differentiate between these conditions. Effective treatment exists for all of them and I see no reason for you to despair.