Car Wont Start

[dkmazza]

2000 S500 - My car is having trouble starting. The key turns but it takes
a few times to turn before it finally starts. I have to wait about 5 minutes
and try and eventually it starts.
When I drive it around and make a few stops I notice that is when it happens the most.
I am 1,500 miles overdue for my maintenance check up. I have changed my gas to regular every now and then instead of premium because of the cost of gas.
I don't know what the cause is. Could it be the fuel pressure and if so do I have to take it to
a dealership to have it fixed or can my local mechanic fix it?

Any response will be greatly appreciated.