Frequent breast/nipple stimulation can produce milk. Your husband sucking breast could be a reason. There are lot many other reasons which can cause this. Are you taking any drugs regularly? I suggest you do a hormone test, Serum Prolactin
. Blood sample should be taken early in the morning ideally on empty stomach. Further evaluation can be done depending on the result.
You using Cu IUD is of so significance here. Need not remove that for this reason.