Personally I think wait until after your 6 week check and then you are the best judge as to when it's right for you. I know people who were back running within 2 weeks and don't seemed to have suffered for it but other friends who have also been very active pre-birth just felt 'wrong' and waited until nearer 12 weeks.
the 6 week check doesn't actually involve any serious checking of your body. so if you already feel fit before it I can't see it would make any difference to wait til a gp has gone through the motions.
I exercised quite a bit from about a month. was hampered mainly by large sore breasts more than anything else - it was not comfortable running or jumping for a while.
Personally this time round I went back to circuit traning classes after 3 weeks. Had a normal delivery, home the same day and felt fine. Laid off ab exercises for a few more weeks, however.
First time round, however, was a bit of a shock to the system (having a baby in the house I mean, not the birth, again normal easy delivery), and felt soooo tired, but I remember I was back in the gym after about 6 weeks.
First time round they kept changing the time and date of my post natel check so I didn't bother going. This time I went to post natel check but wish I hadn't bothered as it was imo a waste of time.
I'd say jst do what you can, so long as you feel ok, but p'haps your physio is advising 3 mths beacuse of ypur spd?
I went to circuit training from a month after dd3's birth, and even signed a form to say I'd had my 6 month check and I pretended the baby was older than she was . but I always feel so much better for a bit of exercise.