First of all i would like to know whether her periods are regular or not?
Second thing with unprotected intercourse
she can become pregnant,and the test comes positive on 22nd -23rd day if the periods are regular,but not necessary ,as if the hormone levels are not upto the mark it might be negative initially.
I would advice you to take up the test again today if she has spotting and if it is negative i would advice you to go for urgent ultrasonography
of the pelvis to rule out ectopic pregnancy
,which is also quite common.
Meet your doctor with the reports as soon as possible.
Don't worry,every thing would be fine.
Dr. Om Lakhani