I use tommee tippee (mostly), avent and dr brown on my baby. She has no problem with switching between different bottles and has always done good with each feeding. Once we moved up to 4 ozs she has started to spit up. She also is very gassy. She will pass gas several times after a bottle, although she did this before moving to 4 ozs. My question is should I switch her to anticolic bottles? We use dr brown and she will spit up and pass gas like crazy after and I thought those were supposed to prevent less air so I'm unsure if it's a bottle problem or not.