My son is losing his ability to walk. Please help.

Hi doctor,

My son is a month away from three years old. Approximately three months ago, he started to lose the ability to walk. He is not able to stand up by making a tripod position. His balance is extremely unstable, and his grip in his hands has diminished that he cannot hold a crayon. When he does walk, he skirts the furniture or refuses and says, ouch. I took him to his primary care doctor, and he ran a complete blood count (CBC) and a C reactive protein (CRP). Both came back normal, as well as x-rays on both ankles and knees. He asked to wait for a few weeks, monitor him, and return if it does not improve. After a few weeks, the doctor himself understood that it had gotten worse from just observing him in the clinic. He again ran another CBC, CRP, and creatine kinase myocardial band (CKMB). All those came back normal. We then got an electrocardiogram (EKG) and discovered borderline right ventricular hypertrophy (RVH). We have an appointment with a neurologist by next week. So, I wanted to head up on the things to ask for, possibilities, and directions on where we go from here. Thank you for your time.