I was perscribed a single 1000mg tablet of Azithromycin (Zithromax). I took it at about 6pm and half way through the night, my neck (sternocleidomastoid near where it connects to my head) was very sore and swollen, my glands dont seem swollen though. Also felt sinus congestion and all around lousy. I have felt this way for over 60hours. Is this a side effect of Azithromycin? Does anyone have any other info for what might cause this?