Baby of 5 months start to eat 3 days ago, she has buttons in the neck and regurgitates more frequently, a mini allergic reaction?

Hello Ma'am,

While I can't see the pimples here, it's quite possible that these pimples are the result of food touching and staying in contact with the skin, rather than an allergic reaction, if they are only present on the neck.

So I would tend to just protect the skin with a pre-meal application of Vaseline™ to the neck.