From what I've seen, you've been using an image to bump your threads. It sounds like you're using the site uploader, which charges 2 TBT for each image uploaded.
To post images for free, use an external image hosting site like Imgur and upload the image. Then copy and directly paste the image's BBCode URL in your post.
Yeah^^ Uploading an image directly from computer/ phone will use TBT each time. I lost a lot of TBT this way :/ what I actually use is Pinterest. Uploading a pic, then linking the image link directly from the pic works great and doesn?t use any TBT!