i'm a 19 year old college student, and i'm on my last 3 days of this medication, and while i had bad side effects at first, i waited them out, and now they're mostly gone. i had stomach cramps, that gassy feeling, i was dizzy and felt faint...i felt like i was in a cloud and couldn't function. however, it was better than the misery i was experiencing from the sinus infection, where i was only able to sleep. i can return to work, and some side effects still linger [stools have a slight red tint to them, stomach rumbling, etc], but its def. done its job as an antibiotic. i did develop a yeast infection from the antibiotic i took before omnicef, which is why i didn't want to change medicines again. i was on another antibiotic, which made me deathly sick. omnicef is supposed to have less severe side effects than other bacterial infection antibiotics out there. i did take a probiotic with the omnicef, i recommend taking one with any antibiotic. it levels out your bacteria levels, which may stop stomach problems altogether.