It sounds as if you were checking prices from two different computers, but if you were using the same computer (i.e. a laptop), clear all cookies when pricing flights.
I don't know if it's still legal or still done, but a report I saw on TV last year (or maybe in 2010) showed that travel companies would show you an initial price, and if you didn't take it soon, they would bump up the price on you to panic you into buying before the price gets worse. This was proven by using a second computer with no cookies and a clean cache and simultaneously doing the SAME search on the SAME website, yielding higher results for the computer that had done a search on the prior day (or even a few hours earlier). This was true for both air carriers and third party travel sites.
I know it sounds crazy, and you'd be tempted to scout the competition to get around it, but the same companies that did this practice would look for cookies from the competition. If you checked out the competition, they would also be more likely to give you a higher price. In essence, there was no danger in giving you a higher price since the competition would also penalize you in like manner.
Again, I don't know whether this practice is still done, but until I find out a definitive answer that it is not, I'd suggest to make sure that when pricing airfare to have all cookies cleaned constantly. The TV report also suggested using multiple browsers to multitask airfare research, since that would curtail the ability to spy on your cookies.
With all that said, a more likely reason you saw the price hike that much that soon could be simply supply/demand for the flights you want. But just in case, clear your cookies and see if it helps.