There's a chance, that your brown discharge doesn't have anything to do with your menstrual cycle.
What's an IUD insertion like?
Troubleshooting your IUD - Mayo Clinic Health System
14 Causes of Breakthrough Bleeding and Spotting
Here's Why You're Spotting With an IUD – Joyja
IUD Removal: How It Works and Side Effects to Expect
Mirena® IUD Safety Data
IUD Removal: What to Expect
Brown Discharge but No Period
I inserted an IUD (coil) a few months ago but keep having spotting. What is the ruling of this blood? - MUSLIMA COACHING
Mirena Weight Gain: Do IUDs Cause Weight Gain?
Brown discharge: What does it mean, and what should I do?
Spotting Before Period Causes & When to See a Doctor