From what you describe it certainly sounds like it has begun fermenting so I would say definetly don't drink it. I can only tell you that I drank some questionable lemonade on one of my fasts and it made me very sick.
Hang in there and drink lots of water till you can get home.
After my episode I only make what I'm drinking the same day and always carry my lemonade in a cooler with some of those reusable blue ice packs. I do squeeze enough lemons to last 2 days at a time but I keep the lemon juice by itself in it's own bottle in the fridge till I'm ready to make my next days batch in the mornings.