After having an open bite before braces, every night when I put my retainer in, it feels tight. What am I doing wrong?
I am glad you are diligently wearing your retainer at night. This is important to keep the teeth from moving back to where they were before. If you just had your braces off, your teeth may have more of a tendency to try to move back because your bone is still in breakdown-buildup mode. You may just need to wear the retainer for more time during the day for several weeks and then wean yourself to wearing it only at night.
If you had braces removed a long time ago, you may want to try to wear the retainer for more time daily.