The most common side effects of Levofloxacin are: nausea, headache, diarrhea, insomnia, constipation, dizziness. Other common side effects include yeast infections, vaginitis, severe itching, chest pain, and swelling from water buildup (edema). If any of these effects last or get worse, tell your doctor or pharmacist promptly. Many people using this medication do not have serious side effects.