Blood stains on the panties but not on the period. If it happens in the middle of two periods, consider that it may be ovulatory bleeding. The estrogen level in the body reaches its lowest during ovulation and bleeding occurs when the endometrium loses the nutritional effect of hormones, but immediately afterwards an egg is discharged, the follicle is occluded, the corpus luteum secretes progesterone, and the endometrium receives the nutritional effect of progesterone, at which point it appears to stop and the endometrium begins to grow further, manifesting only as a transient and slight bleeding. If there is no time correlation, you may also be suffering from endometrial polyps or fibroids, cervicitis, cervical tumor, endometrial tumor or other hidden problems, you need to see a doctor for ultrasound or hysteroscopy to find out where the disease is and treat it in time.