Cough, Wheezing, Feels Like Throat Is Filled With Powder. What Could Be This?

hello iam a 38 yr old woman ,ive had a bad cough for 3 weeks and not bringing up anything,for the last week i sometimes have trouble breathing wheezing badly i feel its my last breath ,sometimes i am sick when coughing also,it feels like my back of my throat is filled with powder when i can't breath. I have been to the doctors and the walk in clinic they say may breathing is 97% and nothing wrong with me , it can be any time i have breathing attacks even getting out of bed could you help me ,as the attacks seam to be more frequent ,thankyou . sarah Baister