What Causes Cough With Phlegmy Throat When Diagnosed With Asthmatic Bronchitis And Sinusitis?

I have been diagnosed with asthmatic bronchitis and sinusitis. I get to coughing so hard I throw up a large amount of clear to white frothy type mucus. What can be causing this? I am on Doxycycline and received a steroid shot and a clindamycin shot. I am using an inhaler every 2 hrs. I sound wet and rattling in my upper chest especially when I lie down. Only diagnosed yesterday. Thank you