What does it mean when you've been late on your period and then start spotting after having unprotected sex?

Weird cycle: It is important to not panic just because one cycle if a little off from the others. The main issue is what is the pattern over time. If your cycles return to normal over the next few months then one abnormal cycle is not an issue. Always make sure your pregnancy test is negative. If you are not on birth control consider starting which will also give you better cycle control.