as you have complain of clear vaginal discharge
but you didnt mention the amount of discharge , if it is scanty it is some time normal. if it is in large amount there is the problem.
If the pregnancy
test is negative, there is no pregnancy but when do you have done the pregnancy test it is important. so if it is too early you will have go for repeat pregnancy test.
and back pain
some times occures before the menses , which is called as pre menstrual tension