Pain! Help!

Okay. So I have this issue that happens every few months or so. 
Basically I get itchy and it's uncomfortable down there. And swelling. There is no foul smell. It's not a sti I got checked for one when I had this issue the first time. But it makes me so miserable. I always just have to suffer for about a week. Then it goes away. The burning and itching is mostly on the outside. Like around my clit. There isn't a pattern to it. And this is like the third time this has happen. I'm on the implant. And I always use condoms as well. Any ideas?