I have a rash mostly under breasts but growing. also, after eating most meals i get an almost instant need to have a bowel movement. ?

Gastro colic reflex: When food normally enters the stomach(gastro) smooth muscle stimulates the colon (colic) to make room for the next items for "food processing" resulting in a urge to have a bowel movement. If the stools are not "loose" or "frequent" as in diarrhea then all is well with the system. The rash cold be a heat rash under the breasts but it wouldn't hurt to have a MD exam the area.