Hi, It's Dr. C. Board certified Ob-gyne with 30+ years of experience. I can provide very detailed information about this situation having managed many many women with similar situations.
I'm sorry that you have this scary bleeding right now. There are a few possible causes. Most of such light bleeding episodes in women into menopause are due to tissue thinning from lack of estrogen. This causes the blood vessels to come to the surface where they can pop and cause such bleeding.
But anytime a woman in your age group has such bleeding, we also need to consider less common causes. These include non-cancrous polyps, cancers and precancers. Some medications and other medical conditions can cause post-menopausal bleeding too. Blood thinners, Tamoxifen and liver disease would be the most common.
The way the doctor will figure out the cause is to take more history, examine your tissues for thinning and most likely have an ultrasound done. Nearly all uterine cancers start along the lining of the uterus. So we take a measurement there. If the measurement is greater than 4mm, the risk of a cancer or precancer is about 10%. In that case the doctor will want to do a biopsy. If the lining is 4 mm or less, they most likely would treat with a very low dose of estrogen placed vaginally to thicken and improve the health of the tissue. This prevents future tissue tears and future bleeding.
Risk factors for uterine cancer include obesity, family history of uterine or colon cancer, no childbearing, a history of skipping many periods at younger ages and diabetes. But even with risk factors present, chances are MUCH higher that it's from low estrogen causing blood vessels to pop and tissue tears.
So the next step is to call your gynecologist or primary care doctor. An exam and ultrasound are typical next steps.
I know it's hard not to worry about it being from cancer or precancer but it's much too soon to say that and statistics are WAY in favor of it not being that. Also if it is, it would likely be caught very early. Most advanced cancers of the uterus occur because women do not seek care for months or even years of abnormal bleeding.
I know this is scary but I hope my explanation has been somewhat reassuring and helpful. Please reply if I can clarify anything or provide more details.