What is wrong with my dog's neck?

First, let me start off by clarifying that we ARE quite sure we are going to take her to the veterinarian; the problem is finding a vet or an emergency vet clinic that are open for 4th of July weekend, so in the meantime we are trying to figure out what might be wrong with her so we can try to help her. My 4 year old German Shepherd dog (about 70 lbs in weight) seems to have injured her neck. I am assuming it's her neck because when she turns her head a certain way quickly she yelps. She will also yelp when she tries to move from a sitting position (on her behind) to lay down on her stomach. Other than these two movements she is able to turn her head in any direction, is able to walk and move around just fine. She is able to walk up the stairs too. It is not a constant yelping or crying, just a brief one when she makes these movements. This dog is naturally a very vocal dog (e.g. she cries and whines about almost everything as if she is trying to talk to us), and yelps and cries often when she gets hurt (even if someone steps on her paw lightly), whereas my other 4 year old dog almost never cries when he gets hurt, unless it's excruciatingly painful. Since it seems that the injury happened last night, we think it may have been when our other dog (the male) and her started rough housing and he tried to jump on her back a bit like he usually does and fell on her neck a bit. At the time it happened she didn't cry or seem to be in pain. We have been giving her two baby aspirin (OKed by our vet in the past) every once in a while (two last night, two with her breakfast this morning, and two more much later on today) to help her with the pain. We are very unsure about how to take care of her, because she keeps following me everywhere I go (as usual) which puts added stress on her injury. I would feel less worried about her moving around so much if I thought it was something less serious, but we just aren't sure. Does this sort of injury sound more like whiplash (from the added pressure on her neck), a strain/sprain, or something worse like a cracked or broken vertebrae?