I seem to have lost at least the last two weeks of email when I switched over from Xfinity to Yahoo on my comcast email account. HELP!

I got tired of the constant messages from Xfinity suggesting that I should switch my comcast email account over to Yahoo, and that it would all be transparent and I wouldn't lose anything. Well, I just did that (on Aug 20, 2026) and now the most recent emails I have are from Aug 6. It seems they lost (??) two weeks of my email! Some of my other folders within that account seem to have lost emails going even farther back. HOW DO I GET THESE BACK? I've got important emails such as doctor appointments, etc... that now appear to be gone. HELP! I wish I had never done this, and instead just switched over to a different email client altogether.