4-8 week olds

What are your 4-8 week olds doing?

My bub is 8 weeks today but 4.5 weeks corrected and is only 3.7kgs. I’m worried he isn’t doing what he should be. He isn’t smiling yet and isn’t great with tummy time and is still very sleepy. He will track faces and toys and make good eye contact though. Curious to know what to expect at this age/his corrected age. 🙂