Welcome to HCM,
As you have not mentioned her date of last menstruation
, it is not possible to say that she can become pregnant or not due to unprotected sex you had with her.
Chances of pregnancy
also depends upon, whether you discharged inside or not while you did it without condom.
In four days, ovum can be fertilised and can try for implantation
. Thus symptoms can be due to pregnancy also.
Loosing virginity doesn't cause backache
etc. after 4 days.
It can be coincidence, but if symptoms persists, she should get herself examined by a doctor.
With good wishes,