This past Friday I went to one of those Physician's Immediate Care clinics (on Adams) because I felt sick. The Doc. thought I had a sinus infection so he prescribed Doxycycline 100 mg (to take for 2 weeks). I felt worse over the weekend and had terrible side effects so I went to a different doctor this week. Well the second doctor told me that Doxycycline isn't for a sinus infection & that instead it is used to treat other things including malaria, anthrax, cholera, chlamydia, syphilis and lyme disease!