I've seen many situations where someone was worried that their email account had gotten combined with someone else's account. (Most of the instances of this worry that I hear about are with Gmail, but the same concern can come up with any kind of email.)
In almost all of those cases, the reason for the concern was that the person was receiving mail that seemed to be intended for someone else. And in almost all of those cases, what turned out to be really happening was essentially the same as receiving wrong-number phone calls: the people who were sending the mail were sending it to the wrong address.
I think one reason that this comes up a lot with Gmail is that Gmail ignores periods in usernames (you can add any number of periods anywhere in your username, and Gmail will just pretend they aren't there), and that leads to some confusion.
Here's an example that might help explain:
Say my name is Fitzwilliam Darcy and my address is firstname.lastname@example.org. Suddenly one day, I start getting mail addressed to email@example.com, and it turns out that that mail is intended for someone named Francesca Itz. And it's coming from several different people—medical records from Ms. Itz's doctor, nude photos from her girlfriend, invitations to family dinners from her stepmother. The obvious conclusion for me to come to is that somehow the system has conflated my account with hers, and that we're both now getting all the mail addressed to both of us.
But in fact what's almost certainly happened is that Ms. Itz has been telling people her address but getting it wrong, essentially the same as if she were to get confused about her phone number and give out the wrong number to people.
For example, her real address might be firstname.lastname@example.org, which she adds a period to for readability: email@example.com. (Remember, as far as Gmail is concerned, fritz and fr.itz are exactly equivalent.) But one day she misremembered her username and started telling people it was f.itz instead of fr.itz. So now everyone who sends her mail is sending to f.itz, which is precisely equivalent to fitz from Gmail's point of view, so the mail is going to me.
So there's no need for me to worry about my own privacy; my mail isn't going to her. (As long as I'm giving out my own address correctly.) It's too bad that her mail is coming to me; I can try to contact her doctor and her girlfriend and her stepmother and tell them about the mistake. But since I don't know her real address, there's no way for me to contact her directly, just like if someone calls me and they have the wrong number, I have no way of knowing the number they were trying to reach.
As noted earlier, all of this happens with non-Gmail addresses too; it's just that the periods add an extra layer of confusion sometimes when it happens with Gmail addresses.
At any rate, if you start receiving someone else's email, there's a very strong likelihood that this kind of thing is why. So don't worry that your account has been merged with someone else's; instead, just think of it as a wrong number.