Where is the back pain specifically? How low down? On one side or both? In the middle or not? Any shooting pains down the back of your legs?
Red flags which mean you need to consult a doctor immediately: problems opening your bladder/bowels (asin physically being unable to do so), difficultly walking because of weakness rather than pain, losing sensation down your legs
Chances are it's muscular, but I'd go to your GP to make sure and that way you can be referred to physio
You can get low strength co-codamol over the counter which you can have with your ibuprofen. Just be aware that it can bung you up and straining can make the back pain worse so plenty of fluid/fruit when you're taking it. And keep active because if you sit down your back will stiffen up and make it more painful