So I've got this f-ing lower back injury. It sucks and I'm beyond p!ssed off about it. I've been down for three weeks now, with only 6 or 7 runs in that time. None since last Monday

I was supposed to run my first ever half this coming Sunday,but it's just not happening.
I'm starting PT tomorrow, to hopefully get me back to functioning. I want to still do a half, hopefully in Vegas on 12/2.
Swimming is probably my best option for exercise right now. I'm going crazy. Is this a reasonable exercise to do with a lower back injury? My docs all seem to think it is muscular, and have me on muscle relaxers to try and combat it.
Water running? Is this a better option than swimming? I gotta do something. I can feel my fitness that I worked my @ss of for this summer fading away, and I swear I'm getting fatter by the moment (

). What would you all recommend? Not working out has turned me into a depressed cranky witch. My poor hubby