Please Help If u Can, question about bronchitis and on med. and might have to get a chest xray help!?

since easter weekend i got a really bad cough and got really really sick monday i went to the dr. and missed skool and the dr. said i had bronchitis so i got some medicine for it like something double strenght that starts w/ a b that i have never taken before but its like 800 milligrams 2 times a day i didn't seem to be getting better almost worst it seemed like so my mom called the dr. today and they asked her a bunch of stuff and they called in a zpack for me and said to take both, so now i am taking both but they said if i dont get better with the medicine that i will probably have to go in and get a chest xray why would i need a chest xray!!!????? thanks please help if you can!