What am I doing wrong?

Friday I went to the gym, did some free weight rows, flys, tricep dips and chest presses with 15s. Then did lateral pull downs up to 70lbs.

My arms were sore but not “can’t lift anything” sore.

I went again yesterday and just a a few lateral rows (50lbs maybe), 5 minutes on the row machine and then 3 minutes of a bench press with just the bar.

Today, my right (dominant) arm is killing me. My left arm is fine. I know it’s hard to tell without watching someone lift but, what have I done to only affect one side? Is there anything I can watch out for or do differently to prevent this?

I’m not a novice but I am getting back into fitness and I’m currently cutting. I was able to do the same lives with 20-25 lb free weights and 90lbs on the lateral machine this winter. I try to be good about checking my form first in the mirror and making sure the weights stay horizontal as I lift.

Any thoughts?