a bit frustrated

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Hi, I am a new member and joined to help me get off my plateau!! in Feb this yr I decided to make some changes, I think I have done it in a smart way but something is NOT working. I kept a food journal for 1 week, if it passed my lips it went in the journal. I then went through it and began making small changes: reducing Mt Dew, Burger King breakfasts, etc., adding more things I should like water. One of the things I realized is I was eating a majority of calories in one meal, I began eating smaller meals. I was getting in 3 meals and on average 2 snacks. I have never been a big rice eater, I didn't have bread for 3 months. I have always steamed my veggies because I love the taste of them fresh, with maybe a little sea salt, no butter. My meat/chicken/pork portions are on average 1 in thick & about the size of my palm. I did a lot of reading on healthier eating and began adding those good habits. I walk 3 to 5 times a week, about 4 miles each time. Now here's the problem: in the first 3 months I gained 12 pounds and have stayed at that for 2 MONTHS!!!! I added more vigorous things to my work out. My walk would go like this: a good 5 to 6 min warm up, run for 1 min, stop and do 15 jumping jacks then run for the remainder of that minute, walk 1 minute, run 1 minute, 15 jumping jacks etc. I am fairly muscular to begin with, so the theory of replacing the fat weight with muscle weight is not true in my case. But I am frustrated to all end. I am NOT giving up, or even close, just looking for some other ideas as to what I am doing wrong. I now have to lose the 12 lbs on top of my original goal. Any suggestions you have please pass my way, and thank you!!! I have not been very detailed on my eating habits, but I don't do cookies, ice cream, chips etc,. I don't eat a lot of processed or preservative filled foods, I eat mostly fresh foods. Don't get me wrong on occasion I do, but mostly fresh foods.