Recently my water pressure starting dropping when the toilet was flushed? This never happened before. I've had a water softener for my house for about 7 years, could that be causing the problem?

How old's your house and what material are the water pipes? Copper? Plastic or galvanized? Does your water softener soften cold water as well as the hot water supply? Back to you, tom

Is the toilet the only fixture that causes you to see a drop in pressure?

If the water to your toiler is soft, I would put the softner on bypass. Most softners have a bypass right where the water enters and exits. Depending on the quality of your water, you may have a plugged softner. Also, galv fittings are prone to plug.