Your baby may cry because the diaper needs changing.
This is the fun part of becoming a new Mom or Dad.
There are lots of opportunities for good stories to tell, and lots of laughs, and the other thing is you get loads of practice, as most newborn babies will pass urine 6 to 8 times in 24 hours. (How frequently your baby passes urine also is an indication of whether baby is having enough to drink, so your baby should have passed urine in the diaper/nappy at least 6 times in a 24 hour period.)
Each baby will deal with a wet or dirty “poopey” diaper differently, but like most of us, we would not enjoy lying around in faeces. Both urine and faeces can irritate the skin, and baby’s skin needs to be properly cleansed or the skin can break down, and your baby may end up with diaper rash/ excoriated buttocks. Same as you, if you had a raw area of skin which came in contact with something acidic (like urine) – it would burn your skin. It’s the same for baby too.
If the skin breaks down it is also then prone to infections, the most common one being a fungal infection like candida. Your Doctor may need to prescribe and antifungal cream is this happens.
You will choose whether you will use disposables or cloth nappies. I have been nursing since before the arrival of disposables, and overall my opinion is that you see less diaper rash with young babies who have disposables. Cloth nappies have come a long way too – and many of the new ones act similarly to a disposable diaper.
As far as frequency of diapering goes, with a poopey diaper, I would cleanse baby’s skin and replace with a clean one as soon as possible. Otherwise, you’d usually be changing the nappy approximately each time baby has a feed (which is roughly every 3 hours). What many Mums do is use a disposable overnight, as the disposable could last 6 to 8 hours. Remember that if urine or pooh is not contained, your baby’s clothes and blankets could become wet, and just as you wouldn’t like to lie in wet clothes – your baby doesn’t like to either.
Each baby seems to have their own tolerance of how long they are happy to spend with a dirty diaper against their skin, before they start fussing and letting you know something is bothering them.