I had period pains, tension, that congested feeling... the full gamut. I just couldn't believe I wasn't getting my period.
They don't tell you that in the books, do they? They always make the symptoms of pregnancy sound very distinct - but in fact the ones they cite are the ones that kick in at around 8 weeks (like nausea). At 4-6 weeks, it's a different kettle.
Are you ttc, Claire?