the pain you are suffering during periods is called dysmenorrhea . its usually in lower abdomen but can also occur in lower back and loss of appetite is a usual feature accompanied with such pains. you should try smooth muscle
relaxants rather then paracetamol
in these situations. there are plenty for dysmenorrhea. but if you are suffering from LBA since 2 months and not getting relieved, see a orthopedician. you may also like to visit a psychiatrist
to get relieved of stress
good luck. stay healthy.