Hi,
I had an injury like yours some years ago, on the last rep of my working set of DLs. I just felt, no, I heard something ripping on the left side, somewhere between the kidney and the iliac crest. I was in a gym, I managed to put the weights away and take the Tube back home. Once the adrenaline rush subsided, I could barely move.
Bending over was very painful; raising my knee, either from a seated or a standing position, was worse.
Started rehabbing after two/three days with long sets of squats, although this is not the only option (here's Alan Thrall's take on the subject: YouTube).
Since then, I've tweaked that same part of my back more than once, although never as seriously, and I am now usually able to resume full lifting in about a week.
To answer your questions:
- it's almost certainly not a disc injury.
- If the above is correct, there is probably nothing a doctor can tell or do to help. Having said that, some foam roller or, even better, tennis ball work will help
- Move. Movement is the better medicine. Let pain be your guide, you will get back to where you were (although IMHO, first time injuries might require a few more days than subsequent occourences).
Last but not least; you probably will get injured again, maybe in the same spot. If that happens, don't sweat, don't panic; you will get back to normal.
Hope this helps,
IPB