Why is it so hard to lose weight?

I've been intermittent fasting for a week and my weight has not budged. I'm 5"10 135 pounds and would like to get to 120. Anybody have weight loss secrets. I'm going to start including a gallon of water.

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Didn't expect to get so many replies... so yeah. I walk about 60 minutes 5-6 days a week. I also have been on weight watchers for about 2 years. now. I was able to maintain a weight of 120 on weight watchers for almost 2 years but it stopped working for me and my weight went back up to 135.
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For those who feel it's hormone related. I have gotten my hormones tested and they're all normal so it's not hormonal.
Why is it so hard to lose weight?
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