S., don't worry that you're being paranoid. There are so many strange flu bugs going around this year, and we are constantly being exposed to bacteria that can cause similar symptoms. My daughter has recently recovered from being exposed to the 0157 E Coli, the bad one known as the hamburger disease. I understand your fear. When I saw blood in her stool I went with my instincts and called the doctor. I'm not usually one to run to the doctor for every little thing, but that caught my attention. If you know your child has eaten tomatoes and you and now he's sick, and if your instincts are telling you it just might not be the flu, then I say get him checked. Call your doctor to check, but you should just have to take in a stool sample. They can tell if it's bacteria or not, but not if it's salmonella at that point. They'll send it to a lab to verify what type of bacteria. If it is Salmonella, the state you're in really needs that information so it can help determine where the source of the bacteria is coming from. So you may want to make a list of everything he's eaten within the last two weeks.
To me the way you say his tummy is bloated and hard, and he's always hungry tells me it may be parasites. I know this sounds awful, but it's pretty common. We have livestock so I'm conscious of that possibility. It's very easy for parasites to transfer from pets to kids, and from meat and fish to people. A stool sample should tell if that is the problem as well.
Good luck and I hope he feels well soon.