You need to go to the DOCTOR - this is not normal.......
The vagus nerve is the tenth cranial nerve and is very, very long. It meanders from the brain all the way to the anal sphincter, where it terminates. When stimulated by a portion of hard feces pressing against the anal sphincter as it is forced out, it reduces the heart-rate and drops the blood pressure. If you already have low blood pressure the additional drop produces anoxia sufficient to cause a black-out. Usually there is a co-factor such as dehydration, anemia or cardiac insufficiciecy to produce a black-out, but not necessarily so. There is a different in genetic sensitivity. The late Jackie Kennedy had a genetically sensitive vagus nerve. This is the the reason many heart attack victims are found dead on the toilet after straining. Isuspect, with your history of excessive bowel movements that you are dehydrated, which is the co-factor. You need to ask your physician to take what are called "orthostatic vital signs" to determine this. In the meantime drink plenty of fluids, specifically electrolytes. There is no cure for this problem (sensitive vagus nerve) except to make sure that bowel movements are not strained. Well, there is a surgical cure, but that is dangerous and rarely utilized. Generally avoiding straining is accomplished by adding a bit of metamucil to the diet. You requirew an evaluation as to the reason for your irritable bowel syndrome and a determination made as to whether this is chronic (as in the case with disease) or merely the result of a problem that can be treated with medication and resolved. Sometimes the irritable bowel is due to an insensitivity to certain foods. You may require a special diet. You need to go to a physician for an evaluation. Pester your mom about this.
No, this is not a joke. There is a condition called defecation syncope (a variation of vasovagal syncope) where people faint when they have a bowel movement. It happens when there is too much stimulation to the vasovagal nerve.
The chronic diarrhea is definitely not normal either. You could have a condition related to your bowels that has triggered fainting. You should definitely ask your mom to take you to the doctor. I would take my daughter immediately if she described what you have said here.