Welcome to imgflip, mate. There's a point system and you'll need more points, I forget how many exactly, before you can add meme to replies. It's not that many, you should be able to get there in a few days, depending on how much you comment and also get commments on your memes. It's good protocol to always upvote a meme you comment on, and always reply to comments made on your meme page. I'll go and give you a bunch of upvotes(if you have other pages) which will get you closer to points enough to commment with memes. Ciao!