Hello,
It is difficult to tell if the lower back pain is related to your irregular spotting / period but it is definitely grounRAB to set up an appointment with your gyne. Ask to have an ultrasound if the gyne does not do it automatically AND you should really have an endometrial biopsy done as well (an in office procedure that takes a small sample of the lining of the uterus). I assume that you are up to date on your pap smears ? If not, then this is also something that should be done (I am sure your gyne will do this automatically).
There are many causes for irregular uterine bleeding including a side effect of using the birth control pill (either at the beginning or if you have used it long term), fibroiRAB, a thickened uterine lining, cervical lesions, thyroid issues etc. You need someone to investigate further. The cause may or may not also be related to your lower back problem.
To try to help yourself re the back problem, try taking an anti-inflammatory to help get yourself moving again. Ironically, if you stop moving, it will often make things worse (move slowly though, don't go running a marathon or anything, just try to keep moving). A warm bath with epsom salts may help as may lower back stretching exercises such as lying down on the floor or on a flat surface and bringing your knees up to your chest. As has already been mentioned, try not to do things that may aggravate the condition. Sit up properly on a firm chair (some easy chairs can make things worse) or consider purchasing a kneeling chair from an office store like Staples. These chairs take the pressure off your back when you sit down.
I hope you get to the bottom of things very soon.
Estria