Running out of steam and more grief about retardation

We just had a bad weekend. My daughter was very sick with high fevers for three days. So now we are exhausted. Therapy has gone by the wayside, and I am just so sad again. Mental retardation is heavy on my mind again. Andy is not learning how to sit up or crawl, and he is almost two. Experts with 30 years experience are saying no sitting up, and continued infant like behaviors are early signs of mental retardation. I don't want to put my head in the sand about this, and pretend he isn't showing all the signs. If I bring it up to family members, they still feel it won't be the case for him. But my gut feeling tells me it is the case. His neurologist feels the same. It just makes me cry,but then I just want to keep moving and not let myself think about it. I try to believe that he can still lead a somewhat normal life, but I don't want to have my head in the clouds. We are just torn to pieces about this.