It's gain has drifted a bit, assuming it was OK when you started using it, of course.
Nothing you can't fix easily.
You watched the levels on your left channel for overs when you recorded. That was good.
Load into Audacity, "Split Stereo Track" into left and right channels.
Amp up the right channel. I like using the "Envelope Tool" for this, instead of having to zero in on a guess for the amount of gain to add.
When you are satisfied, then "Make Stereo Track", and of course, "Save As.."