Had bronchitis almost a month,still have congestion and slight cough, but getting better.is it weird it's lasting so long?

As long as...: If you are getting better symptoms should be resolved soon. Even with a common cold cough can last a few weeks after the initial infection goes away. The airways may remain irritated for a little while which is what causes the cough reflex. I am not concerned as long as you are doing better. If symptoms are not better or worse then it is time to see your doctor again.

Not unusual: It is not unusual for the cough from acute bronchitis to linger for a month. Should the cough not continue to improve over the next 2-3 weeks please see your physician.