Weight-Loss Am I eating enough calories

[Lleonard]

I currently use a Fitbit HR to track my activity and i average 21,000 steps a day, activity 60-120 minutes per day, 4-5 days of running 3 miles, according to the HR monitor on the Fitbit I am in "fat burning zone" about 2-2 1/2 hours a day and eat anywhere between 1500-1700 calories per day (tracked by my fitness pal). I recently came off all medications (anxiety, depression, birth control) and started running as my form of medicine, since this change I actually gained weight. I'm not sure why, is it that I'm burning way more than I'm eating or is it muscle I'm gaining from the running? I've heard you can gain weight if your not eating enough. Oh yeah my Fitbit says I burn anywhere between 2500-2900 calories from midnight midnight. My clothes fit great and I feel like I'm in decent shape but I'm just concerned that I'm harming my body by not eating enough. Any advice is helpful. I can share more information as needed.