In the mess of airline/travel aggregator sites, Google Flights is worth your time. Aside from being a great general starting point for airline shopping, it’s fantastic for price tracking and alerts. Specifically, for a trip you’re planning months in the future, Google Flights allows you to set price trackers for flights within a time frame, or a single flight, and get changes emailed to you as they happen. They also predict whether you should buy today or wait, an important feature, but not always fully reliable (since airlines want to be as unpredictable as possible).
I use Google Flights for all my long haul and more expensive trips, since changes in those prices can mean a lot. You should too, and of course, it’s free.
For in depth discussion of how to make optimal use of Google Flights, here’s The Points Guy’s guide. It’s an amazingly deep and versatile service that gets relatively little press, so the article is well worth a look