I am a first-time mom in need of some help!

My son is 12 weeks old, about 14 lbs, and is breastfed. From the time he was born, I have been told my nurses, family, etc. that he is a very alert baby. Of course, I have nothing to compare to...

Anyway, I feel like he doesn't sleep much and I wonder if his sleep is normal? He sleeps approximately 7-8 hours at night, usually divided into two 3.5-4.5 blocks. A typical night is going to bed at 10:30pm after nursing, waking at 2:30am to nurse, going back to bed at 3:00am, and waking up at 7:00am. A few weeks ago, for about 4 or 5 days, he slept 5-7 hours for the first block, but has since shortened. He sleeps on his back in his crib at night. One positive thing is that he puts himself to sleep at night with no crying. I don't have to rock him. I just lay him in his crib (even fully awake) and he seems to know what to do.

During the day, our very loose routine is to eat every 2.5-3.5 hours, then play, then nap when he seems tired. He will nap for only 30-60 minutes at a time in his crib and will wake up crying. He is clearly still tired, but he will often stay awake fussing and crying for 15-30 minutes before going back to sleep. The exception is if I put him in his swing - he will sleep up to several hours consectutively there!

I guess I thought he would be sleeping longer at night by this age. I also worry that sleeping in the swing during the day will make him dependent on the motion and that maybe being in the swing during the day makes it hard for him to sleep in his crib at night? But he seems so happy and content there...

I would love to hear from some moms who have been through this age. Please let me know your thoughts and any advice! I would also like to know when do babies start sleeping all through the night? Does being breastfed vs formula fed make a difference? Thanks!