Try and follow a structured training schedule, this wil include usually one long run per week, a speed session such as intervals or tempo running and some shorter runs.
I've never used this but just found it, it might be helpful.
http://my.asics.co.uk/my/plan/new
I have followed these plans
http://www.209events.com/file/256.pdf
And generally if you stick to it closely it works.
Its really worthwhile reading the text at the top as well.
The only thing is you will need to be a little careful about injury, don't just steam into loads of training, try a long run at the weekend at say 9 min mile pace and see how you go, endurance is going to be the hardest thing to develop in time for October, I wouldn't worry about pace too much just now as you have plenty of pace for the half marathon distance.
In all honesty it's very unlikely that you will get to run a half marathon at 7 min miles in time so you will need to slow down a bit.
Try the long run when you can, keep it slow which will take some self controll if your used to 7 min miles and reevaluate from there.
Hope that helps.
Jim