I've found that when this happens, it's usually when you upload a photo from one device to another (for me an iPhone to my P.C) if you do it direct from your device it's ok.
The fix that I've found that's easiest is:
- Upload pictures from your P.C by clicking on the "upload file"
-If the picture loads sideways, delete the picture from the post.
-Go to the original photo on the PC (I like to save a copy to the desktop for ease of finding it). Edit the photo by rotating it in the direction to compensate for how it appears on the site. Close the photo and save the changes (even though the photo is now rotated on your PC)
-Open the photo again, then rotate it back to how it originally was. Close the photo and save the changes, now it should appear normal again.
-Upload the file again to your post and it should appear as intended.
I think that by doing this it overwrites the format that was previously utilized by whatever media you used.
I hope that makes sense and that it works for you.