It could be the cold, my 3yo & I have had the same thing, it's not nice & it lasts a while! He goes extremely red in the face like his head is going to explode
Raise the head of her basinette, put karvol or Olbas oil on a tissue in the general area of her bed so it's easier for her to breath at night & maybe go to the dr to get them to test her "snot" least that way you'll know if it's a virus or bacteria or if it's neither to look into reflux, cause around the 5-6 week mark is when reflux usually steps up.