4 week old kitten will NOT stop crying!!

We rescued a kitten who just turned 4 weeks old (mom was killed in traffic)  - she cries during every second she's awake.  She happily eats soft food mixed with kitten formula, she sleeps well, she uses the litterbox.  We give her a lot of affection and attention and she even purrs a lot, but she cries while purring!  It goes on and on all day long.  Is this a phase?? We've only had her 6 days.  What can I do?  Will this pass?

she's a baby, she misses her mom, and her siblings if she had any.

I hope you are bottle feeding her because 4 weeks is too young to be eating strictly solid food just yet (if she truely is 4 weeks) and certainly if you've already had her a  week.

at 4 weeks she is an infant, akin to a human infant, she will need lots and lots of attention especially if she's the only one, you might want to see about getting another kitten for her to have as companionship or see if you couldn't find someone who has a nursing mother with a small litter who might accept her.
 

Has she been vet checked? Wormed? Flea checked? 

A 4 week old should settle quickly, crying all the time is not normal and needs to be checked by a vet.