My baby won’t go to sleep

My 3 weeks old daughter is suddenly very awake and doesn’t want to go to sleep. Used to be easy, feed and she’ll be sleepy and just put her back in cot. Only fusses when diaper is soiled, and when she’s hungry again. Now she’s not having it. She’ll go quiet during feeding and unlatches from the mother after she falls asleep, put her in the cot and she immediately stirs up and cries. Carry her and cradle her and sing to her and she doze off, put her back in and cry again. Checks her diapers and change, feed again in case for comfort feeding. She falls asleep and put her back in cot and immediately same thing happens again. This can go on for hours! Instead of 2-3 hours feeding interval it’s become 6-7 hours of just cradling and re-latching just to keep her at that “sleep mode”. We are at our wits end. Don’t know what to do! #pleasehelp #advicepls