Your Jack is quite a bit younger than my Maddie...she is almost one year old, but she started having problems similar to Jacks at 4 months. She got really sick at that time and put on Prescription diet I/D and was also on medication for about 8 days. She did fine after that, but then got very sick again right around the 4th of July. That time she threw up along with the diarrhea that wouldn't stop. She was on medication but as soon as that was done, her symptoms came back. She then went on the meds again and as soon as they were done, she was sick again. The vet diagnosed her with Inflammatory Bowel Disease and she has been on Metronidazole now for nearly a month. He said she may have to be on that the rest of her life, but for now she is to be on it for a month and then we will very slowly wean her off of it and see if her system can tolerate it. I hope and pray it will work because otherwise she may need surgery to have biopsies.
Anyway, my suggestion to you would be to talk to your vet about slowly weaning Jack off the Metronidazole, rather than just stopping it abruptly. Also, Maddie's fecal floats were negative, but when she couldn't seem to get over the diarrhea, the vet suspected she could have whipworms and treated her with a wormer, just in case it would be that. Whipworms are hard to detect in tests because it doesn't always show up. Here is info on whipworms:
http://www.pethealthcare.net/html/bo...whipworms.html
I sure hope Jack gets to feeling better really soon! It can be such a worry and so frustrating when they get sick and we can't "fix it" for them. Best wishes! Puppy kisses from Maddie!