I have something like this going on all my life. In my 20s I hardly noticed it. I really started noticing in my 50s.
I’ve been able to deal with it with Assos shorts (best chamois ever IMO), liberal use of chamois cream, and an SMP saddle. I’ve also taught myself to pick my butt up off the saddle and center it. Sitting 1-2cm to the right used to feel correct and square. It felt really weird at first but now it feels fine. I naturally sit to the right by 1-2 centimeters and that was causing chaffing on the left which was the first physical problem I encountered.
Remember that you don’t actually sit on the sit bones when riding a drop bar bike despite popular belief. You are really sitting on the center section of your pubic bone (public rami). Measuring saddles by sitbone width is kind of a bogus science. Read these two Steve Hogg links here.
I was also having upper back pain going towards my neck on just the left side. This only showed up after 2-3 hours in the saddle. That seems to have resolved itself with the saddle change plus I started lifting weights last fall.
I got a lightbulb moment recently when I was listening to a Colby Pierce podcast on Asymmetry. He describes the ‘spiral’ movement pattern and that was me to a tee. He was describing a right dominant quad and then a dominant left glute. It’s like our body operates in this spiral fashion to generate power. It makes sense if you are kicking a soccer ball with your dominant foot - kick with the quad, push with the opposite glute.
This lead me to think about how I pedal especially near threshold. I think I lead with the right quad and I just let the left come along for the ride. I’ve since made a conscious effort to not do this during threshold efforts and think of the legs more as equal pistons - left, right, left, right. Just by concentrating on this during a threshold effort I see my power go up by 20 watts since I have a left side power meter.
Since hearing the podcast, I’ve also noticed that people often walk in this one side dominant fashion. They lead with the dominant leg and follow with the other. It’s not super obvious but once you see it, you can’t unsee it. Naturally, we don’t really walk in a perfectly even, symmetrical fashion. We lead with the dominant leg and we cycle in the same fashion.
good listens:
Good luck! I’ve been working on this for like 8+ years.
As far as finding a fitter who thinks about stuff at this level, I’m not sure you’ll find it with the average fitter. My guess is that all the Steve Hogg trained guys would be great. Of course, you could find some bike fit guru somewhere who has trained themself but it’s going to be hard to find.