Think I'm getting close to the best fit, but my elbow is hurting

I've had 2 bike fits with my new Trek 1.5 and I'm in the right position for all the measurements, but until I actually get out and ride I don't realize there are a few tiny adjustments I still needed to make.

I was feeling good until I did a longer 25mi ride last weekend and now my left embow is sore. It only hurts to straighten my arm out and it's mostly sore in the dead center of my elbow. I had a tiny bit of chaffing and sore knees after that ride, but did a small adjustment to my cleats and nosed down the saddle a tiny bit and those have both felt great the last couple of shorter (10mi) rides I've taken.

That darn elbow is still hurting though. Any suggestions on what adjustments to make to remedy the elbow? I prefer to be stretched out and I'm wondering if moving the seat forward a tad at the last fitting has added stress to my elbows or if it was just the longer distance? I do attempt to ride relaxed, but being a new rider I'm sure they straighten out some when I don't pay attention.

I bet you are riding with straight elbows. Keep working to strengthen your core and really focus on your position on the bike while you are riding. Relaxed shoulders, relaxed elbows, relaxed hands. Shrug your shoulders every once in a while, and be light on your hands. Wiggle your fingers. Breathe and smile.

I'm sure the PTs here will have more concrete advice, but do the above and it will help.

By moving your seat forward, you nudged your center of gravity more forward, which puts more weight on your hands to 'hold you up'.
I get that same elbow pain on my one bike- the bike where I feel my weight is centered too far forward. I'm always struggling to keep my weight off my hands on that bike. I always keep my shoulders relaxed and my arms slightly bent to try to help that situation.
When I got my custom bike (a Luna) it was pretty much the same size bike but my weight was balanced and centered better, and no more elbow pain.
If you adjust your saddle back again a little it will center your weight further back again and less onto your hands.
Try riding normally and just slightly remove your hands off the bars by an inch or so- if you start falling forward, it shows you are holding yourself up by having your weight on your hands. See if it gets helped by skootching your butt back an inch or two, as an experiment.
For me at least, weight on my hands equaled pretty bad elbow pain, even with my arms relaxed and bent slightly.

That makes sense. I had no elbow pain until the 2nd fitting. She moved my seat forward some, but the very next ride was the longest one I'd done. I moved it back about 1/2 the distance, but I'll move it back to it's original place where I had no elbow pain.

It's amazing how the smallest tweaks can cause everything to go from good to so bad. And I'm guessing as my strength improves I will have to continue to tweak things.