Hi J.,
With all due respect to these caring moms, be very careful about any advice to medicate your six week old baby, give him any juices, including GoChi and prune juice, and assume he has a disease.
My first question is: what do you normally feed your son? You said "recently...." When did you first notice changes, and what if anything was changed about his diet? The simplest way to deal with bowel changes in a baby is to examine what he is eating and what you are eating, if you are breastfeeding, which I hope you are. Breast milk can prevent the development of most of the allergies we see in children. If you are eating allergenic foods (watch for peanuts, too much citrus, any cow's milk products, nuts, eggs, wheat etc.), you may have to go on an "elimination diet" for a few weeks to figure out what he is reacting to.
If he is formula fed, it is likely he is not digesting something in the formula. Cow's milk is the number one suspect, but children also react to soy, so you'll have to do some investigating. Certain bottles allow too much air to get into his tummy, which can cause pain for him. You might have to experiment with different bottles and nipples. Playtex has one that is a bag you can push all the air out of before feeding, and the nipples have valves so they require more effort to suck, which is beneficial for baby.
Remember that what comes out reflects what goes in. He most likely doesn't have a disease; he has a perfectly healthy body and immune system that is reacting perfectly normally to something he shouldn't be consuming. If you have ruled this out, THEN start thinking about more drastic measures.
Prune juice is too strong for infants. Even watered down, it provides too much sugar for his system and can set him up for candida. Feel free to e-mail me privately if you need to talk further. In the meantime, put your investigator's hat on and start peeling away all the possibilities; I'm certain you will find your answer.
All the best,
S. Waltner
childbirth educator and
post-partum doula