As long as what your son had was just a stomach flu, my understanding is that you should be fine. You'll have to be careful to make sure you don't get dehydrated, drinking whenever you feel like you can keep it down. You also have to be careful about what over-the-counter medications you take; maybe ask a doctor.
Since your immune system is weakened right now, I would definatly suggest calling your doctor and asking what medications are safe for you to take. I had a simple cold that took me 3 weeks to get over; I dont even want to imagine what the stomach flu would do.
As Bxr said, keep hydrated, make sure to eat, and get plently of rest. It shouldnt harm the baby as long as you take care of yourself.
I think you should be fine, my son has been bad with this also its really bad at his school at the mo. I was bad for only 1 day so not too bad.
If you find you are really bad or it has'nt gone within 24 hrs then I would suggest you see your doctor or midwife.