What are some likely causes for these symptoms: 2-5 days between bowel movements, constant nausea and abdominal cramping, headaches, & bloody stool?

Many causes: It sounds like irritable bowel syndrome, but you should be checked by a gastroenterologist. It could be a sign of much more serious problems.

Bloody stools ?: Bloody stool is always a worrisome sign. True, your other symptoms may be functional & blood may be hemorrhoidal or from an anal fissure. However, blood mixed with bowel movements raises concern for ischemia, inflammation, infection. Depending on age, concurrent medical problems, current medications (particularly blood thinners, nsaid's, aspirin), risk factors--be concerned & please get checked.