This is due to improper maintenance of your oral hygiene during your ortho treatment.
Now go for professional cleaning ( subgingival too). Use soft tooth brush and brush twice daily, use mouth wash for 1 week and massage the gums. If the condition didn't improve, then go for laser gingivectomy in particular area alone.
Next Steps
Visit the dentist at the earliest or an periodontist
Health Tips
Don't panic, this is normal and could be rectified within a month .