She sounds healthy to me. If there was a problem, your pediatrician should have said something. My son was 16 lbs. at 4 months as well. He is long so he doesn't look fat. He is now 6 months and I am curious what his weight is. We have his check up next week.
I think this is a classic example of how we are so worried about weight in our society. Poor babies can't even have baby fat or we get nervous.

Tell hubby he needs to relax!