The question to ask is were you engaging in unprotected sex recently and by how many days has your period been delayed?
A late period doesnt automatically mean that you're pregnant, periods can be late sometimes. As for home pregnancy
tests they are always right, they are known to give wrong results every now and again. So either you can retake the home pregnancy test or go to a doctor and ask him to test your blood.
How bad is your back pain? And for how many days has it been aching? If the answer is more than 2-3 days, I recommend you see a doctor.
I hope this answered your question.