Girl, milk came in, I can't get it out completely. Only my little one,…

Girl, milk came in, I can't get it out completely. Only my little one, I have a slight pain under my armpit on one side, probably an extra gland. Has anyone had this? What should I do? She can't drain it or she doesn't have the strength. I think she might be sucking not all of it or the milk comes in too quickly. Help with advice, I forgot everything. Although for the first time such problems don't seem to have occurred