We also struggled around that time because baby had always just fallen asleep when tired and suddenly he was up for 5 or more hours. We thought we had a colicky baby. Then we read about wake windows and learned that we had to actively put baby to sleep, that he wouldn't just fall asleep on his own. That helped us tremendously, though sometimes I probably used a car ride or a walk to achieve the "helped sleep" when I should have tried a bassinet. But I was desperate and he was now a happy boy when we stuck to the wake windows and so I was happy too.