Hey Recursion. I see the Maryland logo. Always nice to meet a fellow Terp!
Like you, I started my comeback after a long break. That was close to 4 years ago. And while everyone is different, the biggest problem I had was trying to play like I used to. My chops were no were near as strong as my memories of what I used to be able to play.
For most of the first year, I limited myself to maybe two 15-minute sessions a day. Any more than that, and I had diminishing returns, similar to what you described. I slowly built this up three 15-minute sessions. At the present time, I practice about 90 minutes a day. (Again, everyone is different. This is what worked for me.)
Early on, I also kept a daily log of everything I played, and how my chops felt when playing. This helped me to figure out what type of playing was helping and what was hurting.
The other suggestions in this thread all have their place, of course. But there's no way to overcome damage from overplaying. So for me, the most important issue has been to know my limitations, and to follow a regular daily routine that I can build on.