my daughter has been really constipated and she is so miserable. she cries till she turns purple and…

my daughter has been really constipated and she is so miserable. she cries till she turns purple and red when she tries to poop and nothing comes out. she is only 3 weeks old anyone have any suggestions? I can't see her doctor till tomorrow. I bought some gripe water but it says ask a doctor before use. any advice to help her poor tummy anyone? I'm desperate