Set yourself a target of a stone, I think a stone and a half is a bit unrealistic. You should be able to do it. I have lost 19lb since the beginning of May - so 11 weeks or thereabouts. I am low carbing and it seems to be working. I have three more weeks before I go on holiday and hope to lose 25lb altogether.
Eat what you normally do, leaving out the obvious bad stuff - cake, crisps, chocolate etc, but cut down your portion sizes. Start by cutting it down a third, and then when you're used to that, try cutting it by a half. Just have half the amount of pasta, rice, meat, potatoes, cheese etc as you usually do. Also, up your intake of water. Make a concious effort to drink a glass of water every couple of hours. And exercise for half an hour every day. If you're struggling with the smaller portion sizes, fill up your plate with salad or veg.