Stomach ache since last Saturday and I ate at a Sonic while traveling by car! Could that be cause? Also dark stools now. Used garden mint in 3 moijtos

Could be. Causes of stomach pain are plentiful. Infection or food poisoning from a meal 6 days prior to onset would likely be associated with some degree of diarrhea and/or vomitting. Gall stone pain, on the other hand and as an example, could have been exacerbated by greasy meal and then persisted. More information would be needed to help. Dark stools are concerning and should be discussed with physician.