Trumpet big problem with air escaping from my embouchure!?

I'm a lead trumpet player in my high school band. Recently I developed an excessive pressure problem because some of the notes I have to hit are at the very top of my range. To fix this, I started practicing with a minimum amount of pressure. My range was a good full octave lower while doing this, but it gave my corners a huge workout. After a few days of doing this, I noticed my lead sound and range had improved.

Now, just randomly, after doing this for not even a week, one day all my lip strength is completely gone. I experience the classic leak in my embouchure where air escapes from the SECOND I begin to play, regardless of fatigue, and my endurance has quite literally gone down to almost nothing. This is clearly a lip strength problem. Is this due to the playing without pressure overworking my muscles? If so, what do I do?? This is extremely stressing, as I need to be able to play.