I had the stomach flu last week also and it was AWFUL!

I didn't get to go to the gym the whole last half of the week. When I felt myself starting to get hungry again, I was like you, afraid to eat. I started with a cup of chicken broth, then a piece of toast. After that it was all good, and by Monday I was ready to work out again. Just take it slowly a little at a time until your back to normal.