从HTTP切换到HTTPS后,PHP会话变量无法正常工作

I recently built a Content Management System, and I'm using session variables throughout my code. However, I just switched over to HTTPS, and now it appears the session variables aren't working.

I've done a lot of research, but unfortunately I haven't found a solution to this problem yet. I'm thinking there has to be a setting in the "php.ini", or the IIS Manager (I'm currently using IIS 7.5) that I'm not seeing.

I found that in ISS Manager, under ASP -> Session Properties -> New ID On Secure Connection defaults to True - I can definitely see that being a problem if it's doing the same thing somewhere with PHP, but I can't find it if that's an option.

I'm initializing the session_start(); at the very beginning of the document (nothing comes before it), and it works fine over HTTP, just not HTTPS. Additionally, I've updated the base_url to include the https:// on any redirects, so it's not going from HTTP to HTTPS, it's strictly going over HTTPS.

Thanks in advance for any suggestions of where I might look.