How long after you ate the questionable food did you start feeling symptoms? There are only two times in my life that I think I was genuinely food poisoned. The first time it was about an hour before I started feeling intense nausea, and my stomach couldn't take any food for a couple days. Then the second time my stomach was feeling "off" within minutes of leaving the restaurant and it was about a 40 minute drive home. The nausea got excruciating to the point that I was laying on my bathroom floor doubled over. My body was desperately trying to expel the contents of my stomach but I somehow still managed to keep it down. Then after suffering from this intense nausea for a few hours, it all came out the other end with explosive diarrhea. By the time the diarrhea stopped it was almost clear like water.
I don't know if this was food poisoning or not but I was in Mexico and had a breakfast at a nice and quite clean looking restaurant. Bacon, eggs, french toast and orange juice. Nothing that would raise any flags. I was almost at the end of the meal when my stomach felt off again and I couldn't finish my last few bites of food. I decided to take a walk down to a nearby beach. It got worse. I took pepto tablets but that wasn't even helping much. Unfortunately I had a plane to catch within a few hours. I had to take a bouncy cab ride over cobble stone streets and somehow managed to keep it down without having the cabbie pull over. Then I had to wait in lines at the airport and then another few hours of waiting before the flight. By the time I got on the plane the nausea was feeling managable, but that was after like 4 pepto tablets. For the next couple days my stomach didn't feel right.
In none of the cases above did I actual vomit even though I easily could have if I wasn't fighting to the death against it. I hear though that some people might take a whole day to show food poisoning symptoms, but in any case where I thought I had it, I knew something was right pretty soon.