Flight prices can randomly drop from time to time, or they can randomly increase as you are experiencing. They can also deliberately drop or increase, particularly as the departure date approaches depending upon whether ticket sales are slower or faster than the airline anticipates (and also depending upon all sorts of other factors, all of which the airline alone will know).

For those of us with a regular route, we know the general price levels and pull the trigger or wait, depending upon whether the fare is a good one or not. If you haven't got a clue as to what the price should be, then it's very difficult, so the only advice left is: can you afford to wait and pay a potentially higher fare? If not, buy now.