Thanks, well 150 grs. for a 4-5 year old snake is very small. Honestly i don't know how to advise you, but at a minimum a mouse every 5-7 days, as others have said. You might get him checked for parasites.
If this were my snake I would feed every five days, check weight after every feediing. I would wait the 48 hours and then make sure he is getting exercise, as you want weight gain but not just fat gain. Keep in mind all of what I say is my opinion only, just trying to give you options, susan