UV fun!

It looks there is a boundary issue where a single polygon or polygon strip takes up the whole UV map itself, or shares the exact same coordinates with others and is trying to merge the results by stretching the UV - you can see the stretched UV texture lines within the strip. 

I see the same thing happening on the tops of the sleeves and the collar. You might try engaging the "Show Wrapping" and "Merge Candidates" in the UV room to discover them. 

Other option: While in the UV room, try highlighting the effected polygons on the model and the perform Operation => Detach Polygons and move the results. This by itself will not fix it but will help you identify the area so you can fix it. 

A helpful thing to do in the future, if you haven't already done it, is to name the selections/polygons so you can use the Detach Polygons tool and easily move things around the map space and then reselect them easily later on too. For example HalterFront, HalterBack, CollarTopOutside, CollarInsideNeck etc. 

Sorry for the generalities. If you post a screen grab of the UV space with all of the polygons showing I can help a little better.

Mark