Just curious, when are you planning on traveling? If you're still about 3-4 months out, fares shouldn't jump like that, but they still can. Generally speaking, about 2 months out, fares spike, and they keep rising until the day of the trip, where either they'll be sold out, be sold at a very high refundable fare, or totally crash because the plane is still half empty.
Maybe you caught a fare sale when you first looked, and that sale had expired the second time. If there's still time to check, try a day or two later, or maybe a week.
The short of it is: airline fares bounce all the time. They want to get a person in every seat, but they want to charge the most that they can for it. If they charge $200 a seat, and the plane fills too fast, that's money lost, as they probably could've charged $300 a seat, and still filled it. But if they set the fare at $300 a seat, and the plane is only 60% full, that 40% empty cabin is lost money. So if a plane is selling seats too quickly, the prices will go up, with the airline thinking they'll make more. If a plane's seats are selling too slow, the prices will drop.
Other suggestions is to try to clear your compuer's cookies and cache, try a different device (a different laptop, maybe your phone on your cell network), or try going to the library. Anything to confuse the airline, and it *MIGHT* result in a lower fare. It might not.
