I am employed in the health care field in Boston... but don't construe this as actually medical advice. More of hypothetical discussion.
(1) You need a new primary care. Have you ever seen them before? A six month wait for an acute visit is totally unacceptable. NOW... if they are just listed on your HMO card as your doc, and you've never seen them... they aren't really your PCP, and maybe they do have a 6 mo wait for new patient visits. In that case, you need to find a different PCP and establish care with them, so when you do have problems you don't have to wait forever. What part of town do you live in? You can very likely find someone with a shorter wait.
(2) I am an ER guy. We see back pain all the time. If you don't mind paying your ER co-pay, someone will be happy to see you... but you are correct, you might wait forever (some places have much shorter waits)... and we won't do much more than re-fill your IBUPROFEN. If you are lucky you might get a quick referral to a PCP or ortho/back doc from the ED, but that does require a bit of luck.
(3) Simple rest, anti-inflammatories, and mild stretching is generally enough for acute back pain to go away. Otherwise, PT might help. Depending on your insurance, you MAY be able to go get PT without A PCP referral. End around the system that way. Same with massage therapy, if covered.
(4) Ibuprofen is over-the-counter. While one cannot recommend long-term ibuprofen without MD supervision, using 400mg OTC Ibuprofen 3 times a day will give you relief. You could even take 600 or 800mg using the over-the-counter pills, though that is more likely to upset the old stomach, and technically is Rx strength.
(5) If you get weakness, numbness, bowel or bladder dysfunction, etc you should ignore everything else and go to an ER pronto.
Anyway, the best thing for you to do, I would think, is to call around and find someone taking new patients more quickly!