Doxycycline
"My doctor sent me doxycycline hyclate for a bacterial infection and after taking it for 5 days I have been having diarrhea on the 6th and 7th day.  I hope that goes soon.  This antibiotic has helped my stuffy and "sneezy" allergic symptoms although on the 7th day I am still feeling and sounding stuffy.  The doctor recommended 10 days of 200 mg each day; 100 mg every 12 hours."