The estimated time remaining will vary up and down as your computer's activity changes. The projection of remaining time is dependent on what the computer is doing at a given moment. The computer has no way of knowing what you will be doing an hour from now; it estimates your remaining time by assuming your level of activity will remain exactly that same as when the estimate is made until the battery is depleted. This is hardly ever true. For this reason, the estimated time remaining is seldom anything you can rely on. A much more reliable indicator of the battery's charge level is the Percentage readout, and I suggest that you change your settings to show perentage rather than time.
Every time you view a web page that has Flash content, even an advertisement that's of no interest to you, your computer's energy usage increases dramatically. Flash is a huge energy hog, and because so many web sites use it, it's hard to avoid.
Again: you don't have a problem.