I had a problem with my daughter (now almost 5) when I tried to get other people to feed her bottles while I was breastfeeding. I breastfed for 11 months and then my nipples tore so bad that I couldn't even pump anymore, but anywho...my milk flow is really heavy and fast, so when it got time for her to drink from a bottle she became very frustrated and would cry and scream instead of eating because most bottle nipples are slow feed. I had to either cut bigger holes in her nipples or buy ones that had multiple feed holes in the tops. Just thought I would share in case anyone else encounters this problem when breastfeeding to bottles. Compare the flow and see if changing it to match your breast more will help. Once I did, she never had a problem with a bottle after.