It's great weight loss - well done! You don't need to speed it up or you just won't be able to keep it off.
You also need to give your body a break. My PT recommends training no more than 5 times per week with gentle exercise on the other 2 days - walking/swimming/leisurely cycle. Your body needs time to rest and recover and it isn't getting any - that's why it's killing you.
I don't think you should speed it up... that very very fast weight loss and I'm not surprised its killing you!
FWIW I lost 3 stone between October and March (and then another half stone since March). I consistently lost 2lb a week.
I went to the gym 3x a week (Sun, Wed, Fri) and then did exercise DVD (shred) or EA sport active on wii 3x a week (Mon, Tues, Thurs). On saturday some walking and exercises like press ups. I dieted eating roughly 1200 a day, low fat, low carb.
FWIW I think you should have a couple of days off the exercise a week - maybe just swim twice a week rather than full on gym session. Also I think if your leg is hurting you should listen to your body and stop running until its better. Again swimming would be good for this.