Lower back pain can be a symptom of pregnancy. Do you normally get it before AF is due - if so, it can also be a symptom of AF coming. If not, then it is a promising sign!
it could be a sign for both af and preg..... so its really confusing.... some months i had it too and got my af... but this month is kinda different...... had severe back pain 2-3 days after ovulations until now...... and am 12 days late..... with 1 negative result....
so its all in the waiting game gurl......
good luck.. and keep us updated!