Sorry to hear that, poor little guy. Hopefully it is something in his diet maybe he isn't getting enough fiber? Sounds like you should find a new doctor, I don't know what tests they can do on toddlers but some one should be able to help. I had some complications from chrons disease and had been taking vicodin which made me a little consitpated and I ended up with a fissure and an abcess on/in my rectum, what you described was similar to my situation there was mucas and even a small bowell movement was terribly painfull it took a while to heal. I don't know if any of that helps, hope he gets better soon.