What Causes A Missed Period With Pain In Back And Thighs?

last month my period came very late and it came in the last two days of the month and lasted for only that two days,and i have not got it as yet for this month.for the past couple of days i am feeling very tired and sleepy,i am having problems with my back with pains going all the way down to my lower back,stomach and thighs.whats wrong with me is this normal???