?

My period was to have started (at least) by Wed. (i.e 4/22). It always varies between 29 and 33 days. Wed would have been day 33. On day 33 (Wed) I experienced light (extremely) spotting and have had nothing else since. I took a HPT (negative) on Wed, the day the spotting occured- the test was taken in the afternoon rather than the morning. Any thoughts on what is going on? When would you suggest I test again? No other symptoms- other than my "PMS" symptoms were heightened this month. Breasts are not particularly sore.