I’ve Been Having Postnasa Drips And A Cold For The

I’ve been having postnasa drips and a cold for the past month and been taking mucinex so my symptoms got better. Two days later, I got woken up by cough due to post nasa drip.. but my chest felt tight and I feel like something is in my throat causing hard to breath and cough. I have asthma and recently just had the baby three weeks ago. I’ve took an over the counter allergy pill everyday.. I don’t know why this cough is reoccurring.. what did I do wrong ?