About a week and a half ago I had to get a tetanus shot because of a nasty cat bight. I have also been taking amoxil for the bight. My period was due to start later that week and at first it did. I spotted for about a day and then it stopped. Then, that Friday it started up again, just enough to make me have to rush home to get cleaned up, then it stopped again. Now, It s starting back up. Is this a normal side effect from such a shot? And before you ask, there is no chance I am pregnant.