You don't have the ability to actually edit questions until you hit 2000 reputation (you have ~450 at this writing). Until then, you can make edit suggestions, which must be approved by (in the case of Stack Overflow) two other 2k+ users, or rejected by two 2k+ users.
You've had a large number of your edit suggestions rejected. Once you've hit a limit, you're prevented from making any further suggestions for a week.
Looking over your suggestions, it looks like a large number of them have been rejected for being too minor. Quoting from the rejection reason, This edit is too minor; suggested edits should be substantive improvements addressing multiple issues in the post. As Lucifer says, adding or removing a tag by itself isn't considered a substantive edit. Look around for other positive changes you can make to posts. They're almost always there.
Take this post at random: lots of juicy product naming issues, and a title that could use clarification.