Thanks everyone so far.
Wow! I thought it was just me that felt a bit of discomfort after a while on the trainer.
My discomfort is mainly in the perineum (which I believe is the name given to the area between the scrotum and the anus.)
After thinking about it a bit more, I also notice some discomfort even at the start of a trainer ride, if I had hammered it the previous day.
Also, as I have spent so much time on the TT bike in an aero position I wonder if this has made a “normal” road position less tolerable for me now.
I had never really thought about standing up for a little bit every 5 to 10 minutes. I always assumed that one should just man-up and grind it out. Anything less is “cheating” etc.
I’m sure that will help a little, but I’m not sure that really addresses the underlying issue.
Over the years and in bike fits, I have noticed/been told that there is a bit more wear in my cycling shorts on the right hand side of the bum and inner thigh. Also the saddle gets worn ever so slightly more on the right side too.
Some said it could be a bit of minor leg length difference, or that it is nothing to bother about as most “favor” one side over an other.
I will check out the rocker plate idea.
I do think that if I got the saddle issue right, it will really improve my training and ultimately my speed. Who would have thought that sitting on a bicycle and pedalling would be quite so technical.