Actually this just happened to me a few weeks ago. I started to spot only a week after my period had ended. I'm on Desogen, and I'm pretty sure it's a low dosage generic as well. My doctor told me that a number of factors can throw off the cycle. For me it was a change in diet/exercise routine. Also I've heard that stress can also throw it off in addition to missing pills, etc.
Were you spotting or did your period actually begin? This can also make a difference.
Don't be freaked! If you're really worried always contact your doctor. I did, and it made me feel 10x better.
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