Low Flow Need Help

I am having a problem with my entire house. If you are using one outlet for water, a sink or shower, and open any other outlet the flow from both becomes almost unusable. This makes showing and washing the dishes or any other task that involve water impossible.

When you first open any valve; hose, sink, tub on hot or cold the initial pressure is high but quickly dies. There are no leaks to be found in the house and the problem seems to be getting worse over the year that I have been in my house. Last summer I was able to run two sprinklers I can now not even run one at a decent flow rate.

Also as the front hose is prior to any other plumbing in the house and is also experiencing the problem, I am led to believe the problem may be with the initial inlet of water.

Any advice where to start my search would be greatly helpful.