My girlfriend is 21yrs old. We had unprotected sex on the 3rd of this month 7 days after her last menstruation day but we used the withdrawal method. Now its been 5 days since the encounter and she has tender swollen breasts. What could be the cause? What are the chances that she is pregnant? I just want to know the possibilities and the odds before she does a pregnancy test. Her menstruation is due in a week.

Chances she is pregnant is just the same as any other time you guys have unprotected sex.

What she can do is:
-wait for her period
-go for a blood test at her doctors. Blood test are able to tell you whether you are pregnant or not a lot sooner than urine tests can.

As far as "what are the odds of her being pregnant?" well it about as possible as finding a penny on the ground. It is just possible.

This is why you should be having protected sex ;)

I hope this is just a pregnancy scare for the both of you. If you can even use condoms as a form of protection I suggest she look for OTHER methods of contraception.