I've had back trouble also diagnosed as muscular, when I lifted something heavy. As in your case I was told to stay active and take ibuprofen. It was bad enough that I could hardly walk.
Unofficially (and I'm not recommending this, though maybe someone with medical knowledge can comment) I was told by a friend who is a physio, to take a fair bit more than the recommended dose of ibuprofen (i.e. 1 gm) straight away when I got the pain, + about 400 mg 3 times a day for the next couple of days. I was told this would be unlikely to cause me any problems over such a short period, though I believe ibuprofen is not recommended if you have stomach problems.
Anyway, I took the ibuprofen and soldiered on, and essentially I was fine within a couple of days.