Okay, here's the situation...

My girlfriend is 4 weeks late. However, she's taken 5, yes 5, home
pregnancy tests and they're all negative; the most recent one being
today. She's not showing any other signs of being pregnant (vomiting,
sore boobs, etc.)

She started a new job about 3 months ago and she works with an entirely
female office. So, she thinks that has a lot to do with it. Plus,
she said she's not very regular anyway. And about 6 months ago she
skipped a month. Also, she's not on the pill but we use condoms. There
was one incident where we didn't use one about 6 weeks ago but not to
fruition.

I talked to a nurse from the Ask-A-Nurse program and she said that she
didn't think that pregnancy was likely at all; especially after 4 weeks and 5
different tests. At this point I'm more concerned than she is (so it seems)
that it could be something serious.

Any advice is appreciated.

Thanks in advance.