I am taking Doxycycline for cellulitis. just for 12 days. I feel like I am dying all the time. Horrible, all over sick I feel sick to my stomach all day. had intravenous anti-biotics 6 times and 11 days on oral Cephalexin 500 and the infection is still here. . If these pills don't kill me before Saturday, I will be finished with them. And I'm not taking a repeat dose. I'm so glad you all posted your comments.