I’ve had back pain since I was a child- mild spina bifida, an old horse-riding injury and big boobs are pretty much the trifecta when it comes to chronic back pain.
If it is a basic musculo-skeletal problem, there is probably some irritation and inflammation. So you treat it like you would any other musculoskeletal problem- rest, ice packs, anti-inflammatories (ibuprofen) and compression.
Basically, some sort of back support belt (should be easily available from a pharmacy), lying on an ice-pack, taking care not to wrench or twist your back further (no heavy lifting either), and taking a few pain pills until things settle down. Walking is great once your back has settled from the inital trauma of whatever you have done to yourself- as long as you have no other problems with your legs or feet.
Although heatpacks might instinctively seem like the best option, they are not. Think of your back as like a sprained wrist or ankle- ice will reduce swelling and inflammation, heat, while it may feel nicer, isn’t actually doing you any good.
When you feel ready, go and see a physiotherapist- they’ll show you some exercises to improve your core muscle strength, without hurting yourself. Do not try to devise an exercise programme yourself or just ask a trainer at your gym to help- the physio will make sure you’re not suffering from something more serious before they start and they know exactly what they’re doing. When it comes to dodgy backs, a physiotherapist will probably be more helpful with regard to exercises than a family doctor.
Long-term, paying attention to your posture, how you lift and move, and possibly a programme of exercise or techniques such as pilates or yoga might be a good idea.
If you have “lightning” type pain or the sensation of “electric shocks”, pins and needles, numbness or tingling in your back or legs or any problems with your bowels or bladder, you need to see a doctor asap. This is the “Do not pass go, do not collect $200” type of “see a doctor asap”- those symptoms suggest spinal cord compression and need to be dealt with urgently.