Hi there ,
As you have been diagnosed with hiatal hernia
you need a periodic medical evaluation.Pains after a long gap in exercise will surely cause pain, which will subside after sometime.
If the is pain very severe you may need painkillers keeping your GERD
and hiatal hernia in mind as the pain medicine can worsen the GERD . Seek a medical attention your doctor can give you pain killers with stomach acid suppressants.Continue light exercises, drink good amount of water .