I'm having pretty bad lower back pain, my period is late by eleven days, and my tummy is sort of acheing, its tender to touch. Is their a chance I'm pregnant?

Any time you have sex, protected or unprotected, there's a chance you're pregnant.

Ask your Pharmacist to recommend a HPT and use it.

You did not say if you had sex or not? If you were having sex, then yes you could be. Have you taken a HPT yet to see any results.