At this age, a young infant needs support with their sleep. Their ability to self soothe, and settle independently hasn't been completely mastered yet.. and what tends to happen is the more they cry, the more upset, overwhelmed, overtired, they become, which creates a completely opposite affect-- they get more geared up and have a harder time to fall asleep on their own.
How familiar are you with Tracy's strategies? Are you familiar with Babywhispering?
Let's start here.