Make sure you aren't locking your elbows, your hands should be able to relax with a light touch on the bars while you are cruising.
I noticed you have your bars above the height of the saddle. If you have to have that position you could set up drop bars so the top of the bar is in the same position and you would gain hand positions as mentioned.
Most of us who ride longer rides have spent time trying different saddles and shorts to find what works for us. Also as others have said you just might need more saddle time to adapt to longer rides.