Girls, what could be associated with bad sleep in a baby (1.5 months)?…

Girls, what could be associated with bad sleep in a baby (1.5 months)? It wakes up every half hour, I rock it - falls asleep and so on all the time. In the previous weeks it was like that too. Then once it sleeps normally, it wakes up every one to two hours. The last couple of days again sleeps for half an hour?