My Baby Two And Half Month Old..she Feed Only Cow

My baby two and half month old..she feed only cow milk... She getting cry a lot of.. When I try to breastfeeding to her.... Now she have lose motion from 3 or 4 days.... I want to do breastfeeding to her... Bt she get irritate a lot and cry.... What should be give her to control lose motion and how I start breastfeeding