Hi!
I'm assuming that since it was 20 months between birth and first menstrual period, you breastfed your daughter for at least some period of time, and perhaps are still nursing.
If so, it is likely that your uterine lining is atrophic or very thin and "raw". That could be the cause of the bleeding and if so, is likely to resolve as your hormone levels return to normal and you start having ovulatory cycles.
It could also be an anovulatory cycle, that would certainly not be a shock given your history. At any rate, I would doubt that anything very serious is going on, and if you were my patient, I would just have you keep track of the next few cycles.
One option to sort things out quickly might be a short course of oral contraceptives.
Hope this helps!
Dr B
thanks for the response! you are right - i did forget to mention that i am still breastfeeding my daughter. i'll watch my cycles and see what happens. hopefully things will get back to "normal" soon, even with nursing (she's cut back a lot and i think that's what started my last menstrual period), as i'd love to have another baby. thanks again!