I have been trying to lose weight for weeks now, have cut out 600 calories per day but no weight loss. Why?

I gained a stone slowly over the last two years. I am now 11 stone and my height is 5 ft 10. I am 32 years old. I have reduced my calories to 1200 daily and am doing lots of walking each week. After 4 weeks I have lost one pound only. My face looks thinner but nothing else, I have lost no weight or inches. I don't understand!! Can anyone suggest? Thanks!

-