Mac is making louder peeping noises now-- not constantly, just when he's trying really hard to stand up, has fallen over, or is experiencing what i can only peg as frustration. He still can't stand on his own, but now instead of standing stick straight in the air and falling backwards, he's tipping over forward and somersaulting, or rolling over onto his back. He can get back onto his stomach at least so I he hasn't gotten stuck on his back.
My gut is telling me that he's having micro-seizures, but I don't know what I can do for him about that... hopefully the B supplement will help. I'll keep you guys posted once I have it.
Silver lining: He slept really soundly last night, so at least he was comfortable enough to sleep.