My one month old baby has a pimple on the same arm she received her vaccine when she was born when pressing it yellow liquid is coming out?

See her doctor: Please have her seen by her doctor. A small lump at the site of a vaccine does occur sometimes, but if there if liquid coming out from it, it needs to be seen/examined. I also do not know what vaccine she had. That would also make a difference in answering your question. At her age, it's especially important to have it checked in person. Enjoy your time with your baby!