+1 on the weight distribution, locked arms and resultant hand pain. There are a lot of nerves running through your wrists and hands. When you have a lot of weight pressing down through them into the bars it pinches those nerves causing pain and numbness. Tweaking your fit and relieving the pressure is the way to go in most of cases.

Also, I'm not talking trash here BUT I know in my areas the Performance shops are good at entry price options but they are often horrid with actually fitting customers. Don't be scared by this though. I just mean that there are tweaks and setup choices they may not have done with you that you can now address and correct if need be. Things like stem length etc that IF are part of the issue you can most likely go back to them and have corrected w/ a swap out.

If there is a chance you can load a photo of you on the bike (preferably locked into a trainer) then some of the kind folks here can better help w/ suggestions...