What do I do? Please help...?

My son is about 1 month old and he is very sick. I believe he has mucus stuck in his chest/throat and he can't cough it up this results in him not being able to breath I try to hold him side ways and pat his back to help him cough it up, no use, I hold him up right and pat his chest doesn't help very much, I blow in his face to help him catch his breath doesn't work. I took him to the ER in the town I live in and they sent us home oh he's ok is what they said, then I took him to his doctor's husband who is also a doctor and he sent us home oh he's ok just a small cold. I'm taking him to the city later today but I haven't got any sleep because I don't know what to do until then. He coughs so quietly from not being able to breath I don't want to take the chance of not being able to wake up. My brother had bronchitis and the doctor said it was contagious but i don't know if he has it and I'm not sure what to do until I take him in any advice?