all thats left to buy is level 3 of medicine and level 3 of fertility... Which one do you suggest i buy first?

Go with fertility. That way you can finish the puzzel's. Level 3 medicine is not all that important, so long as you don't mind losing your villagers at around 70 years of age (or so.)

I think that as soon as everything 'settles down', try to get level 3 for science so that those master scientists can rack up the tech points so you can have some 'choice' on your next high buying decision. It just depends on your game's situation at the time, I know this one all too well...