I experienced the exact same thing you did. Actually, first I went eight months without a period and then it returned for a couple of months. Then I went around a year without a period (not sure exactly how long), could have been longer. I finished hot flashes, breasts became like pancakes, and I even had my FSH tested which conformed I was post-menopausal. Then I got my period again. It freaked me out. It also happened twice, about a year apart. I saw the doctor, both times and both times she ran a bunch of tests including vaginal ultrasound, biopsy, etc. She concluded all was OK and that it's normal to have a few spurts in hormones even after menopause. Still unconvinced, I saw another OB/GYN and he said the same thing. So - according to the doctors - what you are going through can be normal, but you should still check out any post-menopausal bleeding.
I, on the other hand, remain unconvinced about my own situation. For me, this has been going on for another four years (with very occasional bleeding) and pre-menstrual symptoms including bloating and fuller breasts that accompany a high estradiol level than what's normal for someone post-menopausal. For some reason, the doctors don't seen concerned.
Also- this should make you feel better - my dr even told me about a story of a woman who'd gone through menopause several years prior. Then she started dating a woman who still had her period and this woman's period returned! And she was no longer in menopause! So..maybe our bodies are just complicated and don't always fit the 12 month menopause rule.
Good luck!
Even if you did go a full 12 months without a period, it is not all that uncommon to have post-menopausal bleeding especially in the early post-meno years (as many as 5 years). The ovaries continue producing hormones into a woman's 80's and some sporadic estrogen production can cause bleeding or spotting. The breast tenderness and fullness are indicative that this is likely what happened. And then again, you may not even be menopausal. Some women go right up to the 12 month mark only to start having periods again, either sporadically or monthly. However, it is recommended that any post-menopausal bleeding be investigated to determine the cause.
Some medications can also affect ovarian hormones and trigger bleeding. I know women for whom steroids (e.g., prednisone) triggered post-menopausal bleeding.
True post menopause is 12 complete months without a period. Any less time, a woman can have a period and they can be very irradict. If you are indeed post-menopausal, then I would certainly see a gyn, post-menopausal bleeding always needs to be checked.