Our home was built in the middle 70's. Two years ago the hot water tank was replaced. Lately I have noticed (probably the last 8 months or so) but more recently the problem is worse) when I shower that the hot water starts to get cold after 2 minutes of showering. Turning down the cold water helps for a few minutes but then the water gets cold again. Turning down the cold water causes me to have no pressure or very little pressure from the shower head. I have changed the shower head several times but to no satisfaction.