hope you've brought it up to your obgyn! chest pain could be - muscular: expanding breasts (milk ducts forming, mammary glands expand / milk not starting to be produced yet at this stage), or just strained the chest muscles while moving - heartburn-related: acid reflux issues can be common in pregnancy - more dangerous: related to the heart / lungs - I would check it out! take care :-)
it’s too early for chest pain to be related to milk production…. but i guess it’s normal