Haven't lost anything all month..any advice appreciated!

I am 19 and 5' 7". I am committed to working out 3 times a week, don't have time to really do more than that but I won't go less than 3 per/wk. I burn on average 400-420 calories per workout & lift which helps me tone because I was at 209lbs about 2 years ago. 40lbs down, I am now down to 166 but have NOT lost anything all month. I eat very healthy, lots of vegetables & proteins since I lift, while steering away from carbs as much as I can. If i do have candy, etc its occasional/on a gym day where i include it in my calories! I am using the app & alternate between a pattern of 1,540 cal one day to 1,740 calories the next...creating 1,640 as a median. Initially I was eating 1,640 & lost about 10lbs before a plateau. Since then I went down to 1,540 every day for a couple weeks...I lost 5lbs but gained it back. So now I alternate calories & switch up my workouts running 2 miles regularly instead of 1 with fitness videos. I felt 1,540 was TOO LOW for how active I am on my workdays in retail where I run around a store & stand for hours. When I'm not working...I'm a student without a car who constantly walks. I am also waiting for a food scale to come in the possibility that I am overeating! I hope this is true, because idk what is going on. GOAL weight is 130-145. I know that upping calories slightly like I did can result in temporary water weight gain, which happened & is gone now. Once again, my weight has been 166 all month, NO LOSS! I measure everything but I need to be as accurate as possible if I want to lose these last 20-35 lbs. I'd love any help. Thanks!