experienced computer and internet professional with more than 20 years working with computers and internet. When you say all, is it 100% of your mails or a lot of mails are getting into junk? Yahoo does not have Junk folder. Are you using Outlook or some other email client?
I can solve your problem in yahoo mail and you will never again miss a mail form some one for that I need you mail address and password after setting you can change the password.
I'm an Offensive Security Certified Professional, thus a Network Expert. I know the inner workings of an e-mail server, how a browser works and, also, I've had the same problem you're describing. I can help you right away!