The problem, Alsacienne, is that whenever you book - someone else will get it cheaper! Firstly, BA will change their pricing every day if they think they will get an advantage or even by the hour. Their pricing changes depend upon bookings for the specific flight/day/week/month/route AND what the competition are doing and charging. Since we can look at all the competitors - so can they. Other factors include promotions that are global or specific, if there is a big festival or sporting event that coincides with your dates and so the list goes on.
If travelling within the correct margin of days is more important than not going - then you book as soon as you think the price is one that you can accept. After that, ignore that the prices will go up and down, just be glad that you are travelling when you want to where you want. The specialised software called, Yield Management, is far faster and smarter than we are.