This is the advice my breeder and my vet give me for their irregular poop: if they stop eating or drinking, take them in right away!!! If its mushy, it could be too many treats...but if its liquidy they need to go in right away. Is Andy behaving normal or does he seem lethargic? Lethargy is usually a definite sign that its more than diarrhea. If its just diarrhea from too many treats try burning some toast and giving him it, I've heard this helps clear it up. Make sure he is getting LOTS of water. They dehydrate very quickly which can cause them to go down hill very quickly. Acidophilus may be helpful too; you can buy it at any health food store and it helps to restore their natural gut bacteria. Optimus got soft poop when I first gave him raisins. We took him to the vet and they didn't do much except give him fluids and antibiotics. It took about three days for it go back to being a hard pellet. You can give them a pinch of shredded wheat a day and, as you said, I've also heard this helps. I would recommend not giving Andy raisins anymore, ever. They're so high in sugar which can cause severe liver problems. Rose hips and shredded wheat are great treats that won't harm them. So, make sure he's eating/drinking and still playing otherwise get him in ASAP.
Good luck and please keep us posted.