Started as the flu now something more serious

About 3 weeks i started to have a slight cough this then developed into the flu i was out of school for a week and the cough is still here now i went to the doctors about a week ago for an asthma check up (I am slightly asthmatic) and to see if any thing was wrong i do not normally struggle with a cough for this long.

My doctor said that my asthma seems to be improving and that my cough is probably a post flu cough and should clear up soon however if it does not clear up within 2 weeks come back and see me.

Since this appointment i still have my cough and have made another appointment to see my doctor as now when i cough just afterwards i am unable to breath, i would have put this down to asthma but since i was cleared of that i am slightly more worried.

I am not sure whether this type side affect of a cough is normal and have now been struggling to breath after a cough for about a week like i said i have made a doctors appointment for tomorrow but i do not really want to waste the doctors time as it has only been the one week of the two they suggested i waited.