Aloe vera juice is a very mild laxative. I take capsules so I don't really know about the taste.
My daughter was only in the 10th percentile growing up (at 11 she is at 50%). It worried me a little but the ped said as long as she is following the same path and not going down in percentile not to worry about it. And he worried more that a child was gaining in developmental skills, was learning, taking in his environment and growing that way more than a number on the scale. It sounds like your son is close to tripling his weight? Or is my math as bad as I remember?
Kids go through stages where they don't want to eat or eat one thing. If you give him a few finger foods to choose from-put them in ice cube trays and set them out and let him pick the pace at when he eats and what he eats. You'll find that kids that age seem to balance things out on their own.