My DD preferred the right when she was younger, left now. i have read many people suggest that you get bubs checked for neck problems - it may seem all is the same, but it may be uncomfortable for her and she's obviously too little to tell you.

for us, it was the fact that i have flat/inverted nipples and one was easier for her to attach to as a little tacker. she wouldn't want to work harder to get the milk from the other one. now, she seems to prefer that one (possibly because i prefer it to -i find holding her on that side soooooooooooo much easier lol)

have you tried changing how you hold her to feed? instead of cradle hold, try football hold. or even feed laying down during the day?