Google Analytics Goal Tracking an iframe

My website is www.ipodrepairs.ie. I have a number of different order forms on my website. They are all variations on the same google form and are embedded in an iframe on the pages of my site. When a form is submitted a thank you page is loaded within the iframe. It is the same thank you page for any of the form submissions ([login to view URL]). I have installed google analytics code on both the page that contains the iframe and the pages that display in the iframe. In Google Analytics I can see the number of times the thank you page has been viewed. However I would like to track the thank you page as a goal. I have tried this but it doesnt work. I think the problem could be related to iframes. Essentially I want to track order form submissions accurately as a goal in Google Analytics so I can see what referrers result in the most order form submissions.