You have received some great suggestions. In my experience I had a similar problem, yes however due to additional poundage :) , I find that a slight strech by pulling the bottom part of the torso of the suit up makes bringing the shoulders on much easier. I have observed that many divers do this almost as habit and probably don’t realize that they are giving their suit a little tug upwards or performing this strech for the suit as they roll their shoulders.
As the suits are rubber, they tend to compress slightly and so they may seem to fit correctly once the legs are in and you start for the upper body, but in actuality due to the compression they might be a bit ’short’. A good tug upwards for the mid-section helps make the entry for arms and shoulders much easier in my experience.