Weightlifting hurts my back

I think this is a question that you should ask your physio.

Deadlift replacements though:
single leg db deadlift
glute ham raise
good mornings

(unsure if you'll be able to do them)

First determine if it is muscle pain or somethign else. Make sure you are keeping the proper alignment with your back, and that you aren't starting the lift by using your lower back to get the weight off the floor. The movement should be started with your legs.

I asked my chiropractor today, and he said deadlifts will ruin the discs in my low back. That explains why it's been hurting so much! He doesn't want me doing any lifting over my head, either--- no dumbbell presses, etc. It's frustrating when I don't know whether the "no pain--no gain" rule applies, and when to listen to my body and call it quits.

No, definitely go for the 'no pain' rule, if at all possible.

I think it's actually really hard to get good technique. I also think most people will experience injury at one time or another.

For people like us, it's probably a good idea to go remedial for a while. Me, I'm doing Pilates when I can. Getting a grip (so to speak) on posture & core strength will help with everything.

Like I think it's easy for things to go wonky with any kind of big lift if the whole body isn't engaged. Shoulders and lower back will take the pressure if the core isn't into it, or posture isn't right.

Proper deadlift isn't so much a back exercise per se, lifting is supposed to primarily engage the legs (and core, incidentally). But I think, best to stay away from it until you're better generally - i.e., feel NO pain - and have better awareness of your body. That is what I'm telling myself, too And why I'm going Pilates. Though bloody hell, it's expensive

I do have similar problems with my lower back.

Things that I try to avoid:

That woodchopper you mentioned... nope..
Very heavy DL's... here you MUST have a good form or you are asking for trouble.
When lifting weights moving around within the gym, use my legs to lift the weights, not bend and pick the weights with my back.
Anything that would make me feel any stress in any way, I will avoid it, and look for an alternative.
For back exercises, not use my lower back, but isolate to my back muscles.

Yeah... it is "limitation", but not impossible. But like some have said. Form and caution it is key to keep you from hurting your back.

So my question is: what kinds of multi-muscle exercises can I do that won't mess up my back? I'm thinking pushups, pullups (not that I can do them right now), lunges.... other suggestions?

It may be a form issue, as others have noted, but it may also be symptomatic of other problems. I found out too late that I have disc degeneration, bone spurs, and curvature in the spine (not severe like scoliosis, but enough to be a concern.) I have been advised to not do any heavy overhead lifting (military press) or anything else that compresses the spine (squats, deadlifts.)

But there are many many alternatives, even using only bodyweight. One-legged squats in particular - google "pistol squats" for example, and start from a seated position on a bench or chair.

Some of the bodyweight leg exercises I do include wall squats (with an exercise ball), forward and reverse lunges, step-ups on a bench, one-leg "dips" from a bench (not sure if there's another name for them) and the pistol squats I mentioned, plus some others.

Compared to heavy lifting with squats and deadlifts, I have to do more sets and reps to really work the muscles, but it can be done.

Good luck!

Oh, and do lots of stretching after your workout.