I have been taking Doxycycline for only 4 days, already I have had some pretty horrible side effects; vomitting, nausea, dizzyness, shortness of breath as well as being extemely moody and irratable. I wanted to know if these were common side effects among other people of the same age/health as I that have taken this drug. Im fit, in my early 20's and never before have had such a reaction to any drug prescribed to me.