A quick way to check if the seat height and frame size are more or less right, is to look at whether your knee is slightly bent at the farthest part of the pedal stroke (straight down the line of the seat post tube), and if your leg is more or less straight if you put your heel on the pedal at that point. That's just a rough check, but if the answer is yes to both questions you probably don't need a new bike, just perhaps some minor tweaking.