Your doctor is right--some babies are like that! I sympathize with your sleep deprivation. I went through it myself for over 2 years, with my child having GERD and teething pain. And I'm sure it is twice as hard since you also have a toddler. I recommend reading Attachment Parenting and other books by Dr. William Sears. At 4 months, you should be going to your baby every time she cries. She may just need comfort, which is just as important as food. This is too young to be trying the cry-it-out method, which in my opinion is never a good idea, but especially not with babies under 6 months. The No-Cry Sleep Solution is another good book. Some babies have a "high needs" temperament. Baby wearing, such as carrying your baby in a sling, co-sleeping or bed sharing, and nursing are all attachment parenting techniques that are especially helpful with this kind of baby. It is normal for a 4 month old to still wake frequently during the night. Some babies cannot sleep through the night consistently till the age of two. Every baby is different, and as a mother, you have to keep in mind that this won't last forever and that meeting the needs of your babies is your top priority. Try to sleep and nap when they do, and ask friends, husband, and family for help. Good luck!