A woman who tries to raise her catatonic son on her own suddenly discovers a shocking secret about him.

What he said ^^^ (Just pretend I said it first so I look smart)

....and then? This provides a dramatic set-up, but where does it go?

We don't necessarily need to know what the shocking secret is, but we need to know that its discovery will compel certain action - "discovers a shocking secret about him....
"...that she must hide from the authorities or it will tear apart her family"?
"...that she must expose to bring down the military experiments that put her son in a coma"
"...that may not only provide the key to awakening him, but....."

Starting to answer some of that may paint your story a little more clearly.

cheers