For what it's worth, softness is a very subjective concept, and there's no mechanical reason that a fork would get softer over time. The best indicator of a change in the fork is the settle height, or the amount of compression in the fork when you simply sit on the bike. If the spring (or elastomer) inside is fatiguing, it'll let the fork settle lower under normal loads, and as it gets worst will allow the fork to compress to the dead stop (loud clunk, and jolt when it bottoms).

I don't know your fork, but as others have noted, many suspension forks aren't up the rigors of serious technical mountain biking and cannot take the abuse of hard jumps the way "real" forks can.