M.S.
I'm not one to run to the doctor about everything, but an 11-week-old baby who has had a cough for a couple of weeks and is eating less and less needs to get to the doctor, pronto. If she gets dehydrated, she could get much sicker very fast. I have some nutritional ideas I could share that could very likely help with her cough and congestion, but for a baby this young, I think you need to get the doctor's input before trying anything else.