Active female, amount of calories?

Hi guys!!
Okay, so I'm a 19 year old female who is looking to lose a little bit of weight. I am currently 5'4" and weight approx. 140 pounds. I have always loved everything about nutrition and fitness and see myself as quite healthy. Although, when I was younger I did suffer an eating disorder which has ultimately led me to some hormonal imbalances as of currently. I don't really see myself as fat, as I am still quite active. I will participate in disciplined weight training 3-4 times per week, usually followed by 20 minutes of HIIT cardio. On my other days, I like to do at home workouts, go for a run/bike ride/rollerblade, or simply go for a hike. Now I think that I am fit, but I have stayed at this 140 pounds for quite some time now, no budges. I always thought that it was just all of my muscle since I do work my lower body a lot especially. My body feels solid mostly, but I'm just worried that I weigh too much.

On the nutrition side, I've been all over the map. I used to eat alot of fruit and nuts and thought that I was the healthiest soul in the world. Little did I know, I was eating loads and loads of sugar per day, and probably too many calories with the amount of nuts I was chowin' down on. Recently, I've started tracking my calories. I realized that recently before tracking, I was eating probably below my BMR level which is around 1400 calories. I've heard that this can ultimately lead to slow metabolism and storage of fat = weight gain. I got scared, and now am confused as ever.

On my tracking, I am not sure what my calorie intake should really be. I am on the active side, so when I calculated my calorie intake at being "active", it told me 2100-2200 calories just to maintain. Now, I have been no where near that amount of food. So I figured if I wanted to lose 0.5-1 pound per week, I should go 250-500 calories beneath that.
I have decided that I want to eat 1800 calories, at a 40/40/20 macro-nutrient level, and still workout the way that I do. am scared that this will mess my metabolism, or it's too much or little calories....

What should I do in my situation? I would like to get down to about 120 pounds, as this is where I was when I had lots of energy and felt light.. any advice???