pregnancy dunna

i dont know if i am pregnant or not but ive been having horrible back pains in my lower back, they are so strong!!lately ive been more tired then usual and been feeling sick throughout the day for no reason!i was 15 days late then came on my period(sunday) but it wasnt normal it was on for 2 days then off,on tuesday, with light spotting! if i was to be pregnant id be around 4 to 5 weeks!can anyone help xx