I took doxycycline for about 3 months and everytime I would take it I would feel extremely fatigued and lightheaded for about 2 hours. I kept using it for the 3 months despite this because I was desperate for something to work but then I got fed up with it. I began using the oral clindamycin again that I had been using for about 2 years before starting the doxy. I don't think the clinda is working but I don't want to stop for fear of getting worse. I take that back - I DO want to but I'm just scared of getting worse. I don't want to put my body through this anymore. Years of use can't be good for your system.