I don't know your history, but if this is visible blood, and the condition you have been experiencing is getting worse, then a stool exam is necessary.
They should also check blood for elevated antibodies\WB'c
Only really nasty parasites will cause this much blood, but I would not discount it.
If stools have been unformed and loose for any length of time, then stool cultures should be run.
Certain bacterial infections will do this.