She is pregnant or not. Also negative.

I have oral sex with my gf on 24 july i have only fingering.her last period was on 16 july and i oral sex on 24 july.bt she got pain in stomach after two days and after days she vomit only for one time and her period comes on 13 august bt only for two days and her period comes cycle of 28 days.i have four pregnancy test all are negative bt on 23 august she vomit i m very afraid why she vomit. today i have urine pregnat test and this was also negative.she have taken anafortan tablet  for pain 4 or 5 tablet and meprate 10 mg 4 tablet in her anger. IS urine pregnancy test sure to confirm that she is not pregnant or vomit or abdomial pain is due to high dose of tablet. plz tel me she is sure that she is not pregnat because period comes in 28 days bt only for two days