Weaning and hemp milk

I'm full of questions today.

Ethan is officially weaned.  Nursing him for 15.5 months, free of his allergens, is one of the greatest accomplishments of my life.  Being done with nursing him has been bittersweet.  I'm feeling a little regretful about weaning because of his limited diet.  My initial plan was to nurse him until he self weaned or could tolerate milk.  I quickly learned that nursing allergen free through this pregnancy was not going to be possible for me.  I have been sick and NEED to eat.  Being dairy, soy, wheat, egg, peanut, etc free was just too much while pregnant.  Ethan also started to become more demanding with nursing since my supply was so low and my milk had changed.  I worried about nursing a newborn with a tantruming toddler wanting to nurse too.  I've heard success stories about tandem nursing and I wonder if I could have handled it.  Right now, I know I made the best decision for all 3 of us but it's still difficult to swallow when he's not tolerating our ONLY options for milk.

We weaned him from nursing to hemp milk.  I spoke with a nutritionist who felt it would be sufficient as long as he was getting everything else he needed from food.  She preferred prescription formula as our alternative but ok'ed the hemp milk.  Both allergists that we've consulted with have suggested prescription formula.  We tried the hemp milk for a week but Ethan's stomach wasn't adjusting.  I've read that it can take some time to adjust to it but I'm not sure how long to wait.  He went from having 1-2 bm's a day to 4 diarrhea-like bm's.  We stopped the hemp milk nearly a week ago and he's back to 1-2 times a day but it's still diarrhea-like.  We had a stool sample tested and are waiting for the results.  I'm not sure if it was the hemp milk causing the change since his diapers haven't been back to his normal since he had a stomach bug 3 weeks ago.  At first I blamed it on the changes in my milk, then the hemp milk, but now I'm worried something more is going on and the hemp milk intensified it.

We've tried giving him the formulas but he won't drink them.  One is vanilla flavored and not that bad (yes, I tried it) but he still won't drink it.  The other is so nasty that Ethan shivered after taking one sip then pushed the cup away.

I guess I'm writing all of this out to ask for thoughts and experiences.  Do you know anyone who drinks hemp milk?  If so, would you mind asking them how long it took their stomach to adjust to it, please?  Have your kids ever had changes in their bm's that lasted 3 weeks?  Nothing else has changed in his diet and the changes in his diapers began just before we introduced the hemp milk.

I'm at a loss and I don't want to regret weaning him.  I'm very worried.  The only thing he'll drink right now is water.