Hello and thanks for trusting me to help you and Junior today. I am a licensed veterinarian with over 30 years of experience and would be happy work with you.
What it sounds like you are describing is colitis or inflammation of the large bowel. The signs can be very intermittent and could explain why he is normal and then the symptoms return. The signs with this condition can vary in severity, from normal stools to mushy to very soft, all even within one day at times. Seeing mucus or blood is not unusual as well in some cases. There can be a sense of urgency to move their bowels and many of the pets will strain when having a BM, which to the owner can almost look like they are constipated. Many pets with colitis have GI discomfort and some will even vomit.
Colitis can have many causes including intestinal parasites, dietary indiscretion, food allergies or intolerances, metabolic disturbances from internal organ malfunctions, viruses, toxins, cancer or even stress. If this has been occurring regularly, you should at least have him examined by your veterinarian. Your veterinarian will want to know the history of his signs and will need to perform a physical exam to help rule out the causes mentioned. They may perhaps suggest a change in diet or medications. Make sure they also perform a rectal exam to evaluate his anal glands. A stool sample analysis is a very important part of getting to the bottom of this as intestinal parasites are one of the most common causes even if it seems to only occur in times of stress.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.
My posted replies are for general education only and not meant as a diagnosis. Only after a thorough veterinary examination can a diagnosis for your pet be made and specific treatments be advised or medications be prescribed.