It is so individual that it is difficult to speculate. There are so many factors to consider, your current weight, your activity levels and those whilst you are on the plan.
I think that you just need to go with the flow and see how you react to it. I think I was under a stone a month loss but as the weight was coming off I didn't mind that it wasn't as quick as others. It's not a competition after all. Just see it as a loss and the next week will take care of itself.
I think I was abstinant for 7 months and lost 6.5stone.
Your losses are good so far so just keep with it and by the middle of summer you will be all slinky!!!
I lost 4 stone 8 in 12 weeks but it has slowed to about a stone a month now. I work on that figure so I can roughly estimate my end date. everyone is different but as others have said... if you stay in abstinence the weight will come off and come off quickly
I have lost 4 stone in 3.5 months with an average of 3.75 pounds per week. The time has really flown by for me.
As for exercise, I walk about 1 hour per day on the school walk and we usually go for a walk at the weekend, I have a cross trainer which I use occasionally, but that is about it. However, I will now be upping the exercise to help keep it off.