What Could Vaginal Spotting With During Menopause Suggest?

I'm 50 years old and I'm experiencing some light vaginal spotting. I'm going through menopause. Haven't a period for over a year until July 2010. Went to doctor and had a pap smear and sonogram done. Everything was normal. Had a period again in October for 3 days and than again about a week ago with some light bleeding for 3 days and now I noticed some light bleeding again today. I'm currently taking synthroid and other medications. What do you think that can be causing this? Thank you.