Hi! Nice to meet you! That's how old my DS is too, only he wakes up probably every hour to 2 hours to nurse! Out of interest, what does your pediatrician say about sleeping for almost 12 hours at a time without nursing/having a bottle? I was told to wake my baby after 3-4 hours if he hasn't eaten because their stomachs are so small until about 3 months old.
About not sleeping in the afternoon... I just looked at the
National Sleep Foundation's site http://www.sleepfoundation.org/hottopics/index.php?secid=11&id=384 and read that newborns sleep anywhere from 10-18 hours in a 24 hour period, the average is 14.5 hours... if your baby is sleeping from 7:30pm to 6am, and then is sleeping all morning until 12:30pm then you are achieving that range of sleep time - even if the sleep in the morning is broken up. For a newborn it doesn't matter how long a nap is, just that if you add up all their naps it equals over 10 hours of sleep... I feel like my little guy doesn't sleep much because he wakes me up all the time to feed, but I bet if I added up his 30 mins here, 45 minutes there it would equal more than 10 hours in a 24 hour period...
So unfortunately, with a newborn that is the only thing you need to worry about is if they are getting more than 10 hours in the 24 hour period... if they are, then there isn't a sleep "problem" from a medical standpoint, or from your newborn's standpoint either... I'm just reading "The No Cry Sleep Solution" by Elizabeth Pantley (for whom this message board is named) in the section she wrote for 0-4 months and she starts out pointing out that newborns don't have sleep problems; it's us that need to adjust... basically as long as you sleep when your baby sleeps and you get enough sleep, then that is good.
I'm not sure what to say about this situation because most babies this age wake on average every 1.5-4 hours to feed, and then they may be wakeful for a while during that time... but you say your baby is just sleeping straight through. It does seem to be a problem in that babies this age don't tend to be awake for more than 30 minutes to an hour at a time, but now that your baby has used up what sounds like 14+ hours sleeping straight through at night and then all morning, he is truly not going to be sleepy because he's slept quite enough, but he will be quite irritated and overstimulated during the afternoon because that is too long to be awake... maybe I'll e-mail Elizabeth Pantley about this type of situation because I've never seen it before.
I'll try to check into this!

Hang in there!