My four-week-old has a cold?

I took her temperature both orally (said it was 99.9F the first time, and 100.1F ten minutes later) and under her arm (said it was 96.5F, but I think it was mistaken). She's very congested and can't seem to get comfortable when she falls asleep. But when she does sleep, it's for four solid hours, slightly longer than usual. She's eating the same amount as normal and her diaper output is just fine. Is there anything I can do to make her more comfortable or to get her over her cold more quickly?