My 9 Month Old Son Has Been Having Tummy Issues

My 9 month old son has been having tummy issues for a few days now. Now he has a fever of 100.3. He has had to unusually foul smelling orangish loose stools today which was before his temperature went up. He has also been burping very frequently. He's sleeping now and has been moaning in his sleep like he's hurt. Then he burps and the smell is foul and not normal. Could this be a tummy virus? Or something more or less serious?