WATER HEATERS

MY CURRENT WATER HEATER HAS BEEN ACTING UP. THE HOT WATER ONLY LAST FOR A MERE 5 – 10 MINUTES. IN ORDER FOR MY WIFE AND I TO HAVE A SHOWER, WE EITHER HAVE TO TAKE A SHOWER TOGETHER OR LET THE WATER DRIZZLE FROM THE SHOWER HEAD. MY ONLY COMPLAINT IS THAT I WOULD LIKE TO TAKE A SHOWER BY MYSELF AND NOT HAVE TO WORRY ABOUT GETTING A COLD RUSH IN A VERY SHORT PERIOD OF TIME.QUESTION: IS THERE A WAY TO INCREASE THE CAPACITY OF THE CURRENT WATER HEATER?WHAT HAVE I ALREADY DONE TO THE WATER HEATER. I HAVE TURNED UP THE THRERMOSTAT TO HOT. I HAD A GAS COMPANY PERSONNEL COME OUT AND TAKE A LOOK AT IT. (NO SUGGESTIONS) I PLACED A NEW SHOWER HEAD THAT CONSERVES WATER.