Periods After Menopause

Hi, I'm 56 yrs. old. Went from 9/07 to 1/09 without a period. Bloodwork in 9/08 indicated I was menopausal. In 2/09 had light spotting for a week. Saw my gyn who did a transvaginal ultrasound and everything was fine with uterine lining about 3mm. He said if bleeding reoccurred to see him again. In early April, started having breast tenderness and light cramping, just as if my period was about to start. Sure enough, on 4/15 a regular period started, mostly light flow with a couple of heavier flow periods. Flow has lasted (on and off) for over 2 weeks. Since my ultra was normal only a month ago and lining was thin, should I be concerned? I'm going back to see my gyn who will probably do a biopsy. Have talked to lots of women who have had similar experiences. Could this be due to hormone fluctuations and, if so, what can I do to get thru it?