If people are commenting on your memes, there's a couple of ways they are likely to have found them:
1. The memes have featured in the last couple of hours, and they're in the top several pages of Latest.
2. The memes have a lot of upvotes and comments, and they're in the top several pages of Hot.
3. People are coming back to comment on the meme after they've commented previously,through their own notifications, or by looking back through their comments (something each user can do on their profile).
4. People used the "flip" function to go to a random meme, and it landed on one of yours.
5. People clicked on your username from a comment on another meme, or from the leaderboard if you're on it, and visited your profile to see your memes that way.
It's also conceivable that people did a google search for something specific that led them to your image, but I think the 5 ways I've listed are the main 5 ways people would find your memes to comment on them. As far as I know, there's no indication on the site of what page your memes are on, unless you scrolled to that page yourself.