Yes, around the 4 the month, there is tons of brain development. Like the vision changes. Your baby can now see farther away and with all the added detail to her world, she is more perceptive and therefore more distractible. Sleep falls apart and naps are hard to get and often feeding is harder as she is more easily distracted. This is when the baby is ready to lean sleep skills. Previous to this, sleep is innate. Either she can do it or she can’t. Sleep self soothing is a learned skill. This skill enables her to relax and organize her body to sleep when she is tired and it also helps her to better manage her emotions when in stressful situations. Many parents tell me their child’s temper tantrums stop and their child is more even tempered once they are able to sleep without a sleep crutch. So, your child is reaching this time. It’s very exciting and frustrating at the same time. If you want to do sleep training, it’s still a good idea to wait until 6 months if you are going to follow a book. If you need better sleep now, that’s where I can help. To do something gentle like I do, your baby still needs to be at least 18 weeks old and at least 2 weeks into the more distracted phase of the 4 month sleep regression and you would want to have appropriate night feedings as part of your plan. Until you have a plan in place that you feel confident in and can be consistent about, keep doing what ever crutch gets you both as much sleep as possible. Swings, nursing, co-sleeping, rocking etc. these are blessings until you are ready for change. You may want to check out my website www.GetQuietNights.com and read the success stories of parents going through what you are going through. I have recomended books and a blog on there too. Thanks for asking. I wish someone has explained it to me when my babies were that age.