I have had something extremely similar (same place where it hurt, same movements seem to hurt, etc.), also happened during/right after a heavy pull.
I was also stubborn enough not to go to a doctor, as I felt stupid for hurting myself and pridefully decided to fix it myself.
Right after the incident I had to crawl as I couldn't walk, and was pretty miserable for 2+weeks.
So, this is not medical advice (you should probably see a doctor/movement specialist), but I'll tell you what I did.
First: No vertically loaded spine for at least a week. I did not squat or deadlift for a little over a week, and when I did start again loads started light and for low reps per set.
Second: I stretched my hamstrings for 45 minutes+ a day. Really boring, I know.t I sit too much with work and school, and before getting back into heavy hip hinging, I wanted to make sure I could get into a good starting position in the deadlift and actually sit back a bit in the squat.
Third: After 3 days of total rest, I started doing back raises on a GHR. I did sets until my back would be very pumped and borderline painful, rest until pain subsided, then repeat. I was doing anywhere from 100-300 back raises a day, and I slowly began adding band resistance.
Fourth: I hung from a chin up bar for 10 minutes a day. Mostly with a supinated grip, but I don't know if the grip was important.
Fifth: I've upped my trunk/ab training from once every now and again to 3-5 times a week. Lots of ab wheel, "stir the pot", planks, and weighted crunches.
It's been about 4 months since the "injury" and now I have no pain, and my squat and deadlift form feel better than ever.
Again, not medical advice, not necessarily recommending what I did, but this worked for me.