I wouldn't be too concerned, but I would get it checked out.
The blood could be from a polyp in your cervix, or could also be due to very thin uterine lining.
Since the blood could be due to cancer, it's good to have it checked out.
Your doctor would do an exam and see whether there is a cervical or perhaps vaginal polyp or other cause for the blood in the vagina.
Assuming that's normal, an ultrasound can be done. If that shows very thin uterine lining, that would rule out cancer, and we could probably conclude that the blood was from the thin uterine lining.
In case the lining is thickened at all, then you would probably need a hysteroscopy. This is where a scope is put through the cervix to look at the lining. If anything abnormal is seen, a biopsy or D&C could be done.
Just in case there is uterine cancer, it's the kind that we can usually cure by hysterectomy. I think it's more likely that nothing will be found, but time will tell. Best wishes.