If your machine is an electric start model, and has a battery, and if it is 3 years old---it needs a new battery! Those batteries, if used a lot, or twice a week, will not last very long, compared to a battery in your car or truck! I am assuming this machine is a walk-behind lawn mower, as stated. If it is a lawn tractor, the statement above holds true for it, too. Those small batteries, which are used for starting a lot more than the one in your car or truck,usually don't hold up well after two years.

For kicks have a look at the air filter. Are there signs of fuel having leaked into the filter or is it dirty? Model and type # would be good.

Giving it a few days rest doesn't come into play with a lawnmower. Unless it's flooded and the gas evaporates. Does the plug show any signs of being wet? Formerly or currently?