I feel for you hon. I slipped a disc in my lower back several years ago now and it started giving me grief at about 16 weeks. I find that a warm bath (take a book and really relax!) and a heat pack afterwards makes all the difference. When it's been really bad, I've seen my physio and he gives me a really good rub for about 45 minutes. Make sure you're wearing really supportive shoes too. I love flip-flops but they are so bad for my back (I have flat feet as well) so I really need to wear shoes with a very small heel or my runners, which have plenty of arch and heel support.

Besides Panadol, I don't think you can do much for it. I really hope my tips help a little