Is it bad that I've been coughing up phlegm for about 3 weeks now?

Needs Eval. A persistent cough that is productive needs to be evaluated. You may have chronic bronchitis, a form of copd. Other possibilities include bronchospasm of any etiology, gerd, post-nasal drip or even a combination of factors. It needs evaluation so proper treatment can be rendered. If you smoke, you need to quit today!
No. Most likely these symptoms will pass. Allergies have been really bad this year due to the lack of rain.