Burning and tearing pain in lower abdomen rectal bleeding also have anaemia which as been playing up, what can this be?

Abdominal pain: Abdominal pain with rectal bleeding causing anemia needs a work up. It could be variety of reasons, primarily needs to be ruled out for infectious or inflammatory bowel disease.

Need more work up: Rectal bleeding is always abnormal the fact that it is associated with severe abdominal pain requires further work up. In a 16 yr old this might be crohns disease or ulcerative colitis which are inflammatory bowel diseases that may require lifelong management. You should seek out a gastroenterologist for a complete work up