Is it gastroenteritis, cdiff, or celiac disease when diarrhea is accompanied w/low grade temp, head/bodyaches, egg smell and yellowish/greenish stool?

Could be any: Most likely acute infection. Cdiff often presents with bloody stools . Celiac usually does not have fever, but the body can respond in any fashion. If you have concerns see your md and get a stool test and blood test done (blood for celiac) . Stool can rule our cdiff.

Diarrhea: Celiac disease does not cause fever. I do not worry about color unless the stools have blood, tarry color, or acholic ie without color. C diff usually fouls smelling stools as does any colitis.