If her cry is weaker much weaker even if she's eating well, I'd get her looked at if it's been going on for 3/4 day or longer. If she's less in wet diapers, considerably less, or with constant - hours of loose massive poor then get her looked at too. If it's weaker but she's eating well, burping good, pee poo ok and aware then just maybe she's likely ok, just watch her and note down any other changes.
Remember you can check her temp under her arm, internally's best but that's intrusive and hard for baby to tolerate. But about underarm - if she's bundled warm if house is extra warm too then you're gonna get a high temp reading. So if you're house is warm and you don't want to do a rectal temp, then undress her to a t shirt and diaper and let her be like that for a bit, then take her temp. For a one month old a constant of 100, not cooling down dressed less, screaming in pain and/or a weak cry is reason for a trip in.
at 4:03 PM on Dec. 26, 2009