What Causes Severe Itching In The Body After The Removal Of Spleen?

My husband has follicular lymphoma and he has had 8 x chemo sessions. He is now going on the monoclonal antibody treatment for 2 years. He also has had his spleen removed in November. Since November he has had itching like as if he has been stung all over his body and this happens more in the evening and so he has not been able to sleep. He has been drinking heavily each night, originally 1/2 a bottle of spirits, now 3/4 with milk to get to sleep since he says this numbs the itching. He has tried all the antihistamines with Fexofenadine Hydrochloride being the last one. Can you give me some advice as to where the itching is coming from and what he can do to reduce the itching.