refusing bottles!

Juliana
My soon to be 5 month old is mainly breastfed, but has occassionally (4-5 times a week) had a bottle while he is being watched by a relative. Just recently he has begun refusing bottles. He was great going between breast and bottle and never had any problems... until now. We havent switched the bottle and we tried different nipple sizes to rule out flow issues. He currently uses the medela bottles. He has refused the MAM ones and tomee tipee and dr browns from the start. I saw an add for the comotomo bottle and was wondering what people's thoughts were on it. Any further advice regarding why he might have stopped taking the bottle or how to get him to take it again is much appreciated!