How "early bird" plane fares fluctuates and why?

[stevepanas]

I'm getting stucked around those same internet "cheap plane tickets" sites such as:[url]expedia.com[/url] lastminute.com[/url] ;[url]travelocity.com[/url] and whatever could allow a person to book a flight at a price that,in general,should be much cheaper than fares applied by travel agencies.
Anyway last week i begun to plan my next-year holiday,looking first for a flight departing next may 2009 the 26 from italy,(Milan MXP is the most convenient airport),to reach US western coast(SFO,LAS,LAX,SAN).The prices,9 months before, are fluctuating so much and there are so many changes,even between a single day,that it's not that simple to decide when it's the best moment to buy a "NON-REFUNDABLE" ticket for 4 people(me,my wife and my 2 young babies).
Could anyone figure that out how the mechanism that rules those tickets sales works????
And,it would be highly appreciated by me,could a clear explanation be given in order not to make big mistakes????
For exemple since last monday a MXP-LAX ticket for 4 people departing may the 26 and returning on the 12 of june was 1880€ altogether and from yesterday it rised up again to 2450€........
I'm not getting it........
Can anyone ,please, help????