I'm stuck with member's website!

Right Ive researched and managed to create a password system using PHP and a database for my members only site. I'm stuck with one or two more things, so I hope you can help me out. Hope this is the right place to put this.

Basically members sign up to a basic or premium account, I've been able to alter the content they see depending on the type of account with PHP so no problems there. Now every month for a year they will get a selection of photos of my lovely model. Now I only want them to have access to the photoshoots that fall within their membership. So using a database I have put the month they signed up and the month the membership ends and the PHP checks to see if the page which contains this months photos falls within those dates. I can also use a number system like shoot/month 2-13 etc.

All of that works fine but here are the problems I'm now having. I want a page, like an archive page, that displays thumbnails with links to the shoots that they have paid for. Also I want to include the ability to buy individual more shoots which would be added to this page. If they buy individual shoots then the 2-13 thing wont work because say they sign up 10-22 and they buy shoots 2 and 8, how do I include them in the database? Also if they renew their membership then it would be easy to extend it, just put the expiry date a year ahead or add 12 onto the end number.

What happens if they wait a few months before they resign up? They would want to have access to the photos they paid for previously as well as the new ones. I mean if they signed up at the beginning ended their membership at 12 then waited then signed back up at 15. I couldn't put 1-26 because that would include 13 and 14 they are not entitled to.

Is there an easy way of doing this or would I need to put every number or dates into the database like "1" "2" "3" "4" "5", etc instead of doing "2"-"13"

How would I do this? If Im not being too clear please ask me the bits you want clarified.
Thanks
Mike