Well it’s common courtesy on this site to reblog, not repost, and hugely popular tumblrs like fuckyeahreactiongifs have been called out on the same thing — so I would message them and ask them not to repost your work.
I noticed that, too. I was a bit confused since you had just posted it a couple days ago.. They could have just reblogged it instead. Hey, at least it had your name on it! But still.