Sprained an ankle, need help

I sprained my ankle today... for the 6th time...same one. I just started exercising two weeks ago -- 20 minutes daily (7 days a week) at an elevated heart rate like the physical therapist recommended.

Now, I obviously can't do that because -- at this point -- I can barely put weight on my right foot. I still NEED to do aerobic exercise (I know I can do weight training for now too). Any advice as to some aerobic exercise that I could do? I think an exercise bike is out of the picture too, because I don't have access to a gym and I can't put pressure on the foot. Any advice would really help.  Thanks in advance!

This is a stumper.  Swimming would be one that I could think of.  Other than that there is a machine that is like a bicycle for the arms that most rehab canters would have but that's not practical.  I say, "go find a pool".