Thanks sde, nope definitly don't have an index.php in my httpsdoc folder. I am quite sure it is showing my normal index.php page, but is putting a / at the end of it (index.php/) which is why the image links no longer work. I am not sure why its breaking out of what its meant to be doing and showing that page.
I did some testing as suggested. Firstly I created a simple form, that worked fine, so I added more details to it and then all of a sudden it started not working.
Turns out:
If my page is
http://mydomain.com the form works.
If the page URL is
http://www.mydomain.com the form
does not work (it goes to index.php/ rather then the test results page).
Now
http://www.mydomain.com forms used to work fine before I got SSL, so not sure if its PHP related at all. I think the forms are still running through the code properly (storing variables, logging in etc), its just going to index.php/ for some reason rather then the page its meant to. Someone sugguested a htaccess problem, not sure what that means or if its relevant just yet.