My girlfriend and i had sex on a Friday night. The following Sunday night she ate zaxbys and said afterwards she started experiencing nausea & stomach cramps/pains. This was followed by her being tired and saying she didn't feel that good all Monday (slept most of the day). The next Friday has rolled around (about 5-6 days) and she is still feeling nausea and stomach pains(her being tired wore off around Tuesday i believe). She says she only feels this way after eating. she also hasn't ate much at all throughout each day up until this point(abut a meal and a half each day). In particular, she says her stomach hurts only after eating, on the right abdominal side. I haven't been able to figure out if it actually hurt or if its more so cramps. 

Atm im kind of scared. Would she already be showing signs of pregnancy this fast in advance? Or  could it be food poisoning/ another unrelated illness? are these the signs of super early pregnancy? She has about 15-18 day left before her period is due.

I'm looking for insight, and if possible some facts or comments that might calm me down.