My emails and responses are being "stacked". I want them to show individually in the inbox. How do I stop them from "stacking"?

My Inbox has changed.  It used to be that each message that came in was shown separately in the inbox.  Now emails on the same subject are all kept together under one entry.  I have missed several incoming emails because of this.  They don't show up in the inbox if another email has come in on the same topic.  When I try to delete one email in the series, they are ALL deleted.  I want them separate the way they used to be.