In the babylove book, it says that generally newborn babies (0-3months) will sleep somewhere between 9 and 18 hours every 24. Having said that, I'd agree with Shell and ask if you think your baby is getting enough sleep.
Natalie was never a good daytime sleeper, which didn't bother me much at first because she'd sleep well at night. She's only just starting to sort out her daytime sleeps now. I realise now though, that she was generally really cranky because she was overtired. If I were to have that time again, I'd do all I could to resettle her, maybe get a sling to wear her.
Its a hard thing for a first time mum to assess, particularly when you're so tired, but I'd say go with what you feel is best. You are the one who's going to know your baby best.