An unofficial gauge of human misery in the United States rose last month to a 28-year high as Americans struggled with rising inflation and high unemployment. The misery index — which is simply the sum of the country’s inflation and unemployment rates — rose to 13.0, pushed up by higher price data the government reported on Wednesday. The data underscores the extent that Americans continue to suffer even two years after a deep recession ended, with a weak economic recovery imperiling President Barack Obama’s hopes of winning reelection next year.