I would add a probiotic/ acidophilus in your Jack's food. Remember, antibiotics kill all the good bacteria as well as the bad stuff. Probiotic can rebalance the gut and help keep the good bacteria alive. As far as randomly peeing - I have two puppies - a 9 month old and a 14 month old and have been potty training for almost a year straight! My best piece of advice is that sometimes they have accidents, even when they know better. Puppies are so fickle that way! Its smart to call your vet, in case anything is going on, but my guess is that he just regressed a little today. Keep up your training. Your pup will get it!!
