My 12 Year Old Son Is Experiencing Vertigo, Nausea, And

My 12 year old son is experiencing vertigo, nausea, and stomach cramps. He is on MOVICOL twice a day for severe constipation and one week ago was hospitalised for 36 hours for severe constipation, during which time he was given enemas and two full doses of colon prep. He weighs 91 kg and is 5 ft. 9 inches tall. The biggest problems right now are the VERTIGO (he is vomiting, cannot stand any movement at all) and stomach cramps. Still having some constipation. Thank you for your help