Im on my second cycle right now and this exact same thing happened to me like in the 3rd week. My but was swollen for about a week and it felt hard to the touch, thinking that it was an abscess i went to the doctor and told me to get a ultrasound and then told me to take antibiotics, the thing was gone after a week. For the next time you inject yourself i would recommend doing it in the thigh or in the shoulder. It hurts most of the time the day after the injection but if you massage the area real hard after doing it the pain will be minimum the next day.