Deadlifting Injury - Advice Needed

I’m hoping this is a minor injury. It has occurred 3 times in the past 18 months or so, each time while deadlifting. At some point during the exercise (not necessarily when going heavy) I feel a very slight twinge in my lower back, right about at the belt line, to one side of the spine. It is not bad enough to cut my workout short. Then the next day I have a substantial pain in the area. I’m pretty sure it’s muscular.

It feels like it might be a muscle that attaches to the pelvis but I’m no expert. The pain occurs when my spine slightly flexes as in the first few inches of bending over or sitting up. A full bend over seems to relieve the pain somewhat and arching my back seems to relieve the pain as well. Sitting in a chair seems to aggravate it the most. It takes about 10 days to recover from completely, then I’m back to normal.

Does anyone have any insight as to what type of injury it may be? What do you think the cause is? I deadlift weekly without incident and am considered “advanced” by most strength standards for my weight. Could it be from breakdown in form?

Has anyone experienced a similar problem? How did you deal with it? Is there a way to prevent it? Is there a way to know for sure if it is muscular and not spinal?

I have a pretty tight lower back and hams. I have a hard time doing a seated toe touch. Not sure if this is relevant.

I’m without insurance at the moment so I’m trying to avoid going to the doc.

I appreciate any help you can give me. This is a nagging problem I’d like to deal with. Thanks!