I reckon NBB because youve had the pain for a couple of months now that your first course of action is to visit a GP not the physio. Get it xrayed/ct scan (or whatever the doc recommends) and just check there is nothing wrong. The problem with physios is they cant diagnose, they only treat, sometimes they treat the wrong thing. In my case when i really stuffed my back i just went to the physio for a couple of months, then i lost feeling in half my foot and up one side of my leg and could hardly walk. Then i went to the GP and got the scans and the GP told me (like the fella above ) that it was a torn disc. So i payed for two months of physio to hurt me and do nothing towards fixing the problem. Discs from my experience really cause pain when you are leaning forward but your pain seems to be when you extend in the opposite direction so its prob not a disc (it could be a facet joint sprain or a ligament strain or many other things) but still worth getting a proper diagnosis then going to see the physio . I left my problem untreated for too long and payed the price, it took years to get fully better after i had it operated on and i still have nerve damage from it. Its not worth mucking around with if youre prone to back problems. I wouldnt be doing to many painfull ecercises till you know whats not going to cause you more problems.
Once you get a name for your injury then youll know how to treat it, then once you have recovered, get straight into those flexibility exercises and make it your religion
Seriously dont let up on doing them till youre as bendy as jeff hubbard. Thats what i would have told myself way back when anyway.