Why not try keeping a food diary? You need a book showing how many calories are contained in various foods, and a diary or exercise book, and must write down EVERY single item you eat. I have a couple of friends who've done this and they were horrified and amazed at how many calories a day they consumed!
Approximate figures are that a female needs 2,000 calories a day, but if you want to slim, then you need to cut it down to 1,500 a day or lower. Start on 1,500 then work down to 1,200, but no lower. Start doing exercises at least twice a day. Start of with 20 or 30 minutes of gentle exercise to get you into the habit, then extend it to include more vigorous exercise, but always warm up before you start, and warm down when you finish , to avoid muscle cramps and strains.
Doing the above, and not cheating - and that's the hard part - every day, ought to see a fairly steady reduction in your weight. Good luck.