crying and feeling sad

Just had a baby seven days ago and he is so small and handsome 5 pounds and 15 ounces and ive been feeling sad and crying every since i left the hospital i get some sleep and sometimes wake up in the middle of the night to check on him because i get scared that something might happen to him so im just wounding is this normal i have two boys 8 and 14 and when they where baby's never felt like how im feeling now my husband ask me every night am im ok and i just say yes ill be alright but deep down inside im sad scared and overwhelmed...