I've had two different people suggest that the reason I am having miscarriages is because I am still bf-ing Josiah

They said that bf-ing can lower your progesterone levels. Is this just another one of those stupid comments, or do they have a valid point? FWIW, I am not feeling emotionally invested in the bf-ing, never intended to go this long. BUT, Josiah is extremely attached and looks at me like I'm ripping his heart out if I tell him he can't nurse. When we talk and I ask him when he plans to stop drinking Mommy's milk, he matter of factly tells me, "When the baby comes"