Understanding Spotting During the Luteal Phase: Causes & Concerns

Question
Hello,

I am 24 years old.  Last period was May 27.  I took Clomid (100 mg) this month and ovulated on day 15.  

Today, which is 8 days past ovulation, I noticed very light brown spotting on my underwear.  Normally, I would think that this is implantation spotting, but my temperature also dropped today 0.4 degrees (it has been consistently high since I ovulated).

The temperature drop was surprising because I am also taking Prometrium to support my lining.  

What are the possible explanations for this very light spotting?  

Answer
If you started your period on May 27, and took Clomid on cycle day # 5,6,7,8, and 9. (May 31,June 1,2,3,4, you would ovulated on on  June 13. You could have conceived if you had sex on  June 12,13,14, or 15. Your next period is due on June 23 (unless you have a shorter or later cycle). The best time to take a pregnancy test is seven days after missing your next period.  If you do not start bleeding until June 30, take a pregnancy test.