Oh bugger. My lower back right down at my coccyx, has been sore for weeks. My physio glared at me last week and muttered something about possible stress fractures, so I have obeyed him for a change and not run for a week. I see no improvement so far. I didn't even bother going to my GP who has a BMI of about 30. Perhaps that is silly in case I have disintegrated. Regards to your wife. She has my sympathy.
I have never shat so much as since I started running. I need to go at least 3 times before a long run and then afterwards again. A nuisance, but it stops you getting fat. I think it is a mixture of nerves and churning. Onwards and upwards. On my 20 mile marathon preparation run, I needed a poo for the last 17 miles. I treated it as another element of my training. Good luck.