formula help

Chantelle
Hi ladies, 
My 10 week old baby has been formula fed since 2 weeks old (as my milk stopped) I've noticed in the past month her poops have been very dark army green and very thick pastey texture. 
She's had a poop test done and came back all good. 
She's in pain and I don't know what formula is best to put her on as I think it could be th formula, she's on S-26 Original! 
What would you ladies recommend?