I figured you for a predominantly barbell guy. You're doing the right thing by incorporating unilateral and body weight movements. Give those two just as much respect as you did your barbell work and you'd be pleasantly surprised. Not unlike vegetables, those are things you should always include in your lifestyle.
Keep this mind: since the injury, your body has made compensatory changes in the way it moves, sits, stands, etc. This WILL effect even the unilateral and body weight movements. Therefore, UNTIL YOU locate the source of pain, even unilateral and bw movements will NOT yield optimal results.
Most MDs and PTs are (as I stated in another post) pathetically mediocre. I honestly lost track of how many people who have had the same scenario as you. I distinctly remember one of my favorite clients. She is a registered nurse who suffered from chronic lower back pain. The top ortho at the hospital she worked gave some incredibly vanilla advice that got her nowhere.
I still stand by what I said yesterday:
1) Make sure that it's not a case of bulging or herniated disc.
2) Have that right quadratus lumborum checked out by an expert in sports-related injuries. Also have the erector spinae, multifidus, and thoracolumbar fascia examined.
If the cause is definitively not 1 or 2, at the very least we can cross those off our list and move forward. I stated this in another thread; solving chronic pain is often a game of elimination.
A plank is a closed chain bilateral movement. Again, it bears repeating that your body is compensating even in isometric exercises.
As I stated earlier, your body is moving, sitting, standing, etc. with compensatory patterns at this point. Until we know the cause, I cannot recommend a training protocol.
I would prefer to keep it safe and advise you to rest until you get examined for those possible causes I listed above.
If you must do something to preserve your sanity, do the following. Actually, physically write down the exercises you've been doing. Rank them in the order of most provocative to the least. If you can honestly say the exercises on the least provocative section does not cause additional pain, you may - at your own risk - be able to do them AT A VERY EASY LOAD/VOLUME. In other words, just because a certain movement doesn't bother you, do NOT go balls out on them. This is very common error many make.
If you make the mistake taking all that angst out not being able to do your favorite exercises and place that energy (even aggression) into what is deemed as safe(r) exercises, you can very well end up with new set of issues.
I'm going to bust your balls here. Remember my post from yesterday? Here it is:
As I stated earlier, your body is moving, sitting, standing, etc. with compensatory patterns at this point. Until we know the cause, I cannot recommend a training protocol. I'm sure others will be happy to recommend various things you can do. I will not.