what you are experiencing is not normal.You are suffering from Menorrhagia
which causing all the weakness and tiredness
. Your heamoglobin may be low and that causing you all this trouble. You need to consult gynecologist for your heavy menes problem. Low backache
is common in menses but causing disability
for routine activities is not normal. It is called as Dysmenorrhea. The cause of heavy bleeding could be because you are breast feeding or could be some other reason.
Consult your gynecologist for treatment.