Try going off of your diet for a bit. Keep the exercise but stop dieting (continue to eat healthy however). It is probably just too much of a change for your body to absorb all at once and thus you are not getting all of the nutrients you need. Eat any amount of healthy food you feel comfortable with and continue to exercise for about a month to let your body adapt to its new shape and then resume dieting and trying to loose weight.

Also since you have never been less than 165 perhaps that is closer to what you should weight naturally. I am like you; 5'9" and my weight fluctuated between 150-155 in High School and is now about 152-154 after my own exercise and weight loss attempts. 140-170 lbs is a healthy weight range for anyone our height. Ideally I would like to loose another 5 pounds of fat and gain 5 pounds of muscle to hover in the 150 range again but that would be a body I would have to do an inordinate amount of work to achieve and maintain. It is entirely possible that you simply have a larger or denser frame than I do and that is why you weighed 165 in High School and I 150-155.

There comes a time when you have to accept who you are as God made you and learn to be happy with that.

Congratulations on turning your life around and I hope this is a lifestyle you maintain from now on. I hope you do not feel that I am trying to be negative in any way here because I am not and I am sorry if you or anyone else feels that I have been negative in this post. I understand how you might feel, while doing the muscle-gaining phase of my own program I weighed as much as 165-167 (the most I have ever weighed in my life). I did not particularly like it and before I started I had decided that 170 is as heavy as I could ever allow myself to weigh. Unlike you I was not fat but I was terribly weak and could not even walk a block without getting short of breath. Now medical condition or not I can ride by bike at least 4-6 miles at a time with little difficulty at all, and for the first time in my life have some of the health and vitality of a normal person.

Congratulations once again.