I'm really happy for you.It's always really encouraging hearing stories like this. It makes the rest of us persevere and not get weary!
Wintermom, I also have a 5month old baby and I've been doing LR lessons with her and signing as well. I personally think 5 months is way too early to see any signs of what they know now. I know my daughter really enjoys the presentations and that's enough for me now. I guess in her own time, she'll start showing us what she knows. It's just like talking, I believe at this age, they're already acquiring language, they understand a lot of what we say to them, but they can't talk back. A few months to come, they'll start revealing to us what they know. So I won't worry at all.
Wintermom, rest assured that NOTHING is wrong with your child! 5 months is WAY too early for him to demonstrate what he have learned.