I.S.
Babies are physiologically made to sleep in REM throughout the night in order for brain reparation. All day long they are bombarded with a million new sensations, pictures, words, motions, sounds, movements, etc etc etc etc. During naps they are so PHYSICALLY exhausted so they sleep in DEEP sleep. At night though, their brain puts their body in REM or light sleep. That is the only sleep in which their brains can repair, sort out new information and build new cells. Any noise, even their own breathing, can wake them from this. It's unfortunate but it is how they develop!
Also, babies are more comfortable with mom and or dad because during the day you give them comfort and reassurance. At night, alone in their crib, they don't get that which is why it is so difficult for them to get back to sleep after the inevitable waking.
What we have done is put a toddler bed with one side as a crib (so he can't roll out) pushed against the bed, so the open side is flush with our mattress. He sleeps there next to us. He still wakes and cries but it is so easy to console him and he's back in dream land in the blink of an eye!
Remember, it won't last forever and you're DEFINITELY not alone!