Hi, if you take birth control sometimes you don't have the right dose (usually not enough hormone in the pill) you get spotting and sometimes a full period at the wrong time. If you are not on birth control you might want to get your doctor to do a pelvic exam make sure nothing is wrong. Otherwise, I guess it can happen. I agree the cramps and back pain are usually related to menstration.
mkh9
this is probably just simply cramps. period craps cause pain in the back, and the lower stomach. this is no big deal. its part of being a woman! :) so get used to it! hahah! and if the pains are really bad, taking some pain medication wouldnt hurt. they have some medicine that is made just for cramps! check it out at the pharmacy, or the closest drug store. i personally find that "MIDOL" (pronounce: my-doll) works the best! and its quick too! i hope this helps! have a happy period. :)