.

Hi... you might find this article informative https://sg.theasianparent.com/tips-on-getting-your-baby-to-sleep-longer

My 3weeks baby also the same. Handcarry her she sleep very soundly. But she awake immediately when put her on the cot.

Hey , The baby is very much used to your body's warmth and smell. Hence better would be to take a nap with the baby

Try sleeping with her when she is napping. She may wake up crying as she misses the smell and comfort of your body

Are you breast feeding? Latch on demand. Do also check whether she has colic, n urine n poo Color.