Metronidazole
"I have had a terrible experience with this drug. First night I took them I started getting light headaches I kept going for three more days before I realized it was the drug. I stopped for one day, my headache cleared up after 24hrs, I started them up again. I was fine until today the second day in the headache was there again, lightly at first but for the last 6 hours it has been a nightmare. I feel like my teeth are trying to get into my brain. 

They've also caused insomnia I can't sleep for more than 2-4 hours at a time."