Hi Nick and welcome to our group,
If you have had chronically low Hb levels for many years I would suggest that you have the possibility of extramedullary hematopoiesis investigated. When the bone marrow cannot produce enough good red blood cells, masses sometimes grow in the body that will create red blood cells to supplement what the bone marrow is producing. These masses are called extramedullary hematopoiesis and they are frequently found in the abdominal cavity, where they are sometimes attached to organs, liver and spleen in particular. In addition, these masses can cause moderate to severe pain because of pressure they exert on the spine. When they press on the lungs, breathing can become difficult.
The reason I bring this up is because of the pain you have experienced. Your doctor may not be aware of the realtion between thalassemia and extramedullary hematopoiesis, so it should be brought to his attention and if it is a possibility, diagnostic tests should be done. This is sometimes treated with either blood transfusions, which reduce the growth of the mass, or chemotherapy, such as hydroxyurea, which can shrink the mass, relieving the pressure that is causing the pain. In extreme cases, surgery may be required to remove the mass. You may need to see an experienced thal-familiar hematologist to diagnose whether this is the problem