Have been latching my lo ( 3 week plus) for two and half hour already.. lo will fell aslp on my nipple but when I bring her to the cot she will Wake up and cry and stick out her tongue and appear hungry.. what's the reason behind it

Comfort latching. Needs nipple in the mouth to sooth to sleep. Frankly anything u do now will mould a sleeping habit. When baby stop suckling actively to drink unlatch baby and hold baby for a while and then put down. Try ur v best not to rock. Another way is to unlatch and put a pacifier in immediately. Or u can encourage baby to suckle thumb or something.