You cannot please everybody, so they say. Just let them be. They are everywhere. It's a sad part of this world. Continue writing good ones and they might get bored in flagging.

I'm not so sure but I think there are also bots who do that. I'm pretty new here just like you.

Just be sure all your articles are yours including the images you used. Site or quote your sources whenever you have to avoid more of them who downvotes.

Bots like @steemcleaner flags as well and if they do, it's bad. You need to contact them on #discord for disputes.

Cheers buddy!