IT seems from your descriptions that you've experienced bleeding from the anus (rectorrhagia). The most common reason for rectorrhagia is hemorrhoids... but anal-rectal fissures, colon tumors and inflammations (colitis) can also cause blood in the stool. You must visit a doctor for a physical examination and to request an occult blood test first. Additional procedures like an abdominal ultrasound scan and a colonoscopy can be done later if necessary.
You can also take a home pregnancy test to confirm or exclude pregnancy as a reason for the lack of menstruation (amenorrhea).