I noticed couple of blood drops 2 days ago in the morning (this was about 5 days earlier than my usual menstrual cycle).  I had unprotected sex with my husband that night assuming that it was safe.  Since then, I only noticed another couple of blood drops yesterday & today.  I am curious if I should take the Plan-B pill to prevent pregnancy (I could wait another 24 hours as the window to take the pill is 72 hours).
Hi, as per your history you had sex in safe period. This bleeding can be an abnormal start of your period, or it can be a sign of early pregnancy or, if not because of these two, it can be contact bleeding because of some pathology or infection in cervix. If you don't want pregnancy, then you must go for emergency contraception immediately. Although time to take Plan B pill is 72 hrs after having unprotected sex, but its efficacy decreases as the time interval increases. So, in my opinion, you should take one as early as possible.