The reason for a "range" of developmental timing as to when a baby "should" be doing these things, is because each baby is different... they are not all the same in development. However, the "range" is what is considered "normal" per pediatric time-lines.
IF a baby, does not do certain "milestones" by this time or is perhaps 3 months 'late' in doing so, then perhaps there is a concern.
BUT, go according to your Pediatrician.
There is also a difference between "milestones" and just developmental changes that occur.
Don't expect EVERY SINGLE thing to occur in your baby like clock-work. It won't. It won't. It won't. ALL babies are this way and have their own timing and pacing and development.
Bear in mind that the eye development in 1 month old's (the rods, cones and color) perception is NOT even fully developed in a baby this young, yet. What they "see" at this mere age, is dark and light "contrasts" in shapes.... and their smell is more acute... that is how they "recognize" their Mom from others for instance.
A baby does NOT 'see' as we do... it is developed over time, nor can they 'see' over long distances, for example.
Try getting the book "What To Expect The First Year", which you can find anywhere and online.
AND, check out the website: www.babycenter.com which is EXCELLENT. Here is a link:
http://www.babycenter.com/0_your-1-month-olds-development...
Those are the 2 sources I would rely on, other than your Pediatrician.
Main thing is, don't feel 'rushed' that your baby has to develop at a certain pace, nor 'compare' your baby to others, and do NOT "expect" more than the age of a baby. Keep all expectations "age-appropriate. I just say this because many times, Parents "expect" a baby/child to be and act like an older child, unknowing that it is too much too soon. Thus, disappointment/frustration/stress can occur, when it does not have to. Or they get worried if their child/baby does not do things like others. No worries. It's okay.
ALL babies, develops differently.
If your Doctor is not worried, then don't worry. They know best. Of course if you feel your baby is not developing on par, then ask your Doctor or give him/her examples.
Many babies at this mere age, mostly sleep and nurse. They are not going to stay up playing all day. Their "job" is to sleep and nurse... because even sleeping aides in brain development and overall development. Sleeping has a purpose too. And, nurse/feed ON demand... because this provides the "building blocks" for a baby's development as well.
Please, I know how you feel... but don't worry. If ALL babies developed exactly the SAME... then that wouldn't be 'normal' either. Each baby has their own personality and development. Right now, a baby just needs to be nourished and cuddled and spoken too... but babies this young also get fatigued very quickly from over stimulation. Even 1 hour of "playing" is a long time for them. Let him sleep when he needs to sleep....
Its okay. I'm sure your baby is fine. But I can relate to how you feel. I felt like that too, with my first child.
Well sorry for rambling or getting off subject.
All the best,
Susan