Hard starting and extremely poor high gas mileage

For about a year now, my highway driving gas mileage is around 19 or 20 mpg and it used to get 32 mpg. It seems the car is hard to start (meaning, turns over more than it should) before the engine starts. And once it does start, it sounds like the engine is flood but it does run. The other interesting point, is at times (once a month, twice a month) the gas mileage will come back for 3 or 4 days and then go back to poor fuel economy. I drive on a rough dirt road, but this does not seem to affect this coming and going. Also, the engine runs smooth once it's running and this does not seem to change when the gas mileage returns back to normal. The car seems to start quicker once the mileage is back. Can you please point me in the right direction on possible causes for my car acting this way? Thank you