MC joint pain on middle finger one hand

I'm an active male in my 40s.  In April of this year I woke up the day after working out at the gym (not sure it's related) and my middle MC (knuckle) joint on my right hand hurt badly.   I could barely make a fist.   After weeks of trying NSAIDs and immobilizing it and icing, I had an Xray which showed nothing broke and no signs of OA.  The dr. gave me an injection of Lidocaine and something else (not corticosteriods) and it was fine for about 4 months.  Now it has started hurting again.  The pain is movement based.  Mostely flexion and side to side.  What else could it be if it's not bone?  I work at a computer all day, so this is my mouse hand.  Any ideas what this could be?  I have to type at work so it's not something I can immobilize long term.  Not sure what to do next.