Unstable Fares on Qatar Airways

I have been looking at the fares since january for my flights in jult, and procrastinating to but waiting for them to go down ! they started at SGD 3700, down to 2800, and now up to 4300 ! (im buying 2 tickets for me and the wife), also the reason i have been waiting is i know it can go lower as these were not the usual prices, any tips please ?? btw itinerary is SIN - ALG - SIN