Answer
It is natural for adult men and women to have wet dreams. If wet dreams are caused by stimulating the mind and soul with evil, for example, looking at nude/semi-nude pictures, fantasising, etc. then that is from the Shaytaan.
It is in that context, Rasulullah (Sallallaahu Alayhi Wasallam) said, ?Wetdreams is from the Shaytaan?. It is possible that frequent wet dreams is due to the above mentioned point. If not, it may be due to weakness.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai