Shauna, you can switch back and forth... I wouldn't reccomend it to much... Might upset the babies tummy... Depends on the babies... Sometimes with formula babies can get constipated (sp?). Breastfed babies have an easier time with pooping.. Thier bms are almost like brown urine and they have a sweet smell to them, in the begining anyways
i would reccomend nursing at least until 6 weeks, thats when the baby get the most nutrients and what not from nursing, than if you wish.. Start switching back and forth at that point.. But unless you really need to I would just stick to nursing. It's healthier.
I will say though.. Nursing might hurt alittle in the begining.. But don't give up! Your nipples will have to toughen up alittle in the begining... And for about 2 weeks they may be really sore... If they are unbareable I would consult your lactation consultant at the hospital you deliver in b/c baby may not be latched on correctly or may have thrush or so on so forth.
I wish you the best of luck feel free to ask me any questions you may have!