Dang nab it

Well, as often happens in life....
Two steps forward and one step back...
I have been enjoying? my work outs lately with P90. My wife has been doing most of them with me and is actually pushing me at times which is great.
Last week our son Ryan was in town and him and I did a workout together, his workout.
I attempted to do some squats with about 120 lbs. on the bar, not a lot of weight, but I have been doing lots of squats in the P90 program without weights, along with lots of lunges. My plan is to get ready to go into P90X in September or October.
Well, after doing the squats with the wights, my left knee swelled up, not too bad, but...
So, I am cruising along with my workouts, losing about ten pounds, looking fitter and feeling great, muscles getting some definition and tone, and Monday night, my wife and I did a sweat workout and my knee is now really bothering me. Feels like it did years ago when I went in and had it scoped.
My plan is to lose enough weight to give my knees some relief and this happens...
I am pretty bummed about this.
Just getting going, and wham!
probably gotta take a break and I don't want too.