Suggest Treatment For Stomach Pain Due To Giardia

Hello there, my son is 7 and has a long history of food intolerances and allergies. He is anaphylactic to cashew nuts, but is also allergic to other tree nuts. He has allergies to eggs, dairy and wheat as well. He has had severe and ongoing tummy pain for about 3 months now. We have had many investigations. we found that he had giardia which was treated with antibiotic, but there was no improvement. He then had other tests and ultrasound scans of tummy and pelvis which did not show up anything. He then had an x-ray which showed that his entire colon was impacted and he was severely constipated. Our paediatrician told us to give him osmolax 2 scoops, 3 times a day until he had diarrhoea for 4 days and then have a repeat x-ray which we did. He was still impacted. He has just spent 4 days in hospital last week having a bowel washout. He has had another x-ray and is now clear, however he is still sick. There has been no improvement and he is still suffering from the same tummy pain. What should we do next? Concerned Mum