blood transfusions can sometimes cause immunity problems which lead to the body attacking itself, causing inflammation and such, if that's what your concern is.
i read that somewhere..i know that's not specific, but do a net search and you will find info.
so it is possible that the transfusion could be causing inflammation leading to loss, but don't rule out other causes (psychosomatic etc) just because i mentioned this.
i'd see a doctor if you are really concerned..obviously.
you can get supplements to balance assist with immunity prolems.