Slightly elevated CA125

For nearly seven years, I have been screened every six months with a CA 125 and a pelvic ultrasound including intravaginal. I have a history of endometriosis. In May 2003 I had a CA 125 of 12.6; this November it's 36, although ultrasound results show no fibroid growth and no issues re the ovaries. I am aware of the limitations of the CA 125 but since I have a sister who died from ovarian cancer, any fluctuations above the so-called norm of 35 -- and specifically a jump like this when I normally register a 12-28, raise my antennae. I did have my period the day before the blood was drawn as well. My doctor has asked that I repeat the CA 125 the first week in December and has indicated that she suspects endometriosis as the cause for the blip since ultrasound looks good. Is it normal to have 20 odd point fluctuations like this and still have nothing wrong? Or should I be more concerned than she seems to indicate?