Hi. Samuel's mum has offered some great advice already. I would just like to add that at 4 weeks old, you and your lo are still getting adjusted, and this is a time for you to learn about him. Are you keeping a log of his feeding times, and when and how long he naps? I feel that would be a great help. It is very common for babies to have short naps b/c some lack the ability to put themselves back to sleep after the sleep cycle ends (40-45 mins). This is especially true for babies that are used to being fed or rocked to sleep. But don't fret, I rocked my dd to sleep, too, until 6 months to be honest, and then I was so frustrated that I couldn't handle it anymore. I used pu/pd, but at his age, you'd probably need to read about shh/pat. I suggest that you find The BW Solves All Your Problems book for more details. Until then, go through the Naps board and I'm sure you'll find many, many posts about short naps, using shh/pat, and how to hang in there. It can be challenging and time consuming, but it will be very worth it.
As for the feeding frequency, it is advisable to listen to your ds's ped., but if he is continuing to gain weight and is in good health, I don't see why he couldn't be on a 2.5-3 hr feeding routine. If you feel that he is ready for that, you can use a paci/soother to try to comfort him and help him last a bit longer before the next feed. Sometimes, a need to suckle is mistaken for hunger and that can often lead to snacking. I'm not saying at all that this is what is happening, just that is can happen. But if you move to 2.5-3 hr feeds, he may start taking more full feeds and will be able to last 2.5-3 hrs on his own. Just remember, though, that a baby's tummy is very small and there is a limit to how much they can hold and some become hungry sooner than others.
Again, just try to relax and enjoy your baby. Things will fall into place, but we're so glad you joined us! The BW methods are so very beneficial and practical. I hope some of this helped. Please continue to let us know when and how we can help.