First thing is always the
Numb Hands post. Notice how far forward these riders are reaching.
then
Bar Positioning -make your bars look like that.
Then try moving your saddle all the way back. See how that feels. Your hands should be light on the bars and your elbows well bent, elbows right behind your hands, not sticking out the to the side. With these adjustments, your hands should be light on the bars, the heel of your hand resting on the bar tops and taking the hand pressure. Looking in a mirror while you are on the bike leaning against something, your upper arms should be making about a right angle with your torso. You may need a longer stem - stems are cheap. I suggest getting rid of the shims and putting on a -17° stem that's long enough to establish that 90° upper arm/torso angle. If you can't get that angle with say a 110mm stem and the saddle all the way back, the bike is too small.