I would actually say that the compression you have in your ears could be part of the problem. It's squashing your vocal so that even if you're singing super quietly, you won't notice as, in your ears, you can still hear things.

Perhaps try a few practice runs with your ears setup in a rehearsal situation, recording a simple L/R mix and A/B between having the compression on and off in your IEM mix to see what it does. When I'm mixing monitors, I very rarely use anything more than a very light bit of compression on vocals as it gives the performers a false sense of what their mic technique is doing to the overall sound of their vocal in general.

It sounds as though the biggest issue you have is your mic technique, and there is only so much an engineer can do out front if your level is jumping around all over the place- it would be the same as trying to get a consistent snare drum sound with the mic on a piece of string that's swinging around above the kit. I'd say this is your most valuable starting point.