The last few years I've had a lot of trouble with the frettin' fingers. They got really bad for awhile.
A few things that helped:
* I switched to light strings. I still prefer the sound of mediums but the luthier showed me on paper who much more psi it takes to press the mediums down. Couldn't argue with that.
* I started concentrated on not pressing as hard. Press down only as hard as you have to to get a clean tone. I had to practice that a lot- and I'm still not cured of that bad habit.
* I stretch my fingers and hand before and during when I do any serious playing. One of the easily controlled methods is to straddle the fingers over the left leg, easing them apart. A few minutes of that gains me added mobility and flexibility.
* I simply don't play as hard as I did. I've discovered that I don't have to play every single song or tune that someone is playing. Nowadays I get a lot more fun out of just listening. Sometimes when there are people in the circle who are used to watching hands to see what chords I use, I will make the chords (air guitar!) with the hand but not even touch the strings.