My 3 wks old cant sleep, helppp?

ok so im starting to be concerned. my 3 wks old baby is up most of the day and most of the night. all the newborn i know of sleep a lot, mine doesnt. i make sure she is full and clean, i give her baths rock her feed her and she dozes off to sleep and as soon as i put her down she is up wailing. this is the case both for day time and night, i am exausted. but more concerned because newborns are supposed to sleep a lot, right? not mine though, she is up like 7-10 hours straight!!! is this normal? what could be going on? and how can i get her to stay asleep once i put her down so that she sleeps longer than half an hour. like for instance, today she took her last nap at 12pm and has been p since, it is now 7pm, the only other time she slept is like a half hour nap while i fed her, then i put her down and she woke up within 5 minutes. is this normal? please help me i am so stressed out and exausted all at once.