The reason that you have to log in to everything again is precisely because you cleared all your cookies which, as well as other things, are used by web apps to allow users in without having to log in every time. However, once you've logged in once, you should get in without logging in next time - unless:
1) you have somehow turned off your browser's ability to save such cookies - unlikely;
2) you have not clicked on the equivalent of "Remember me" when logging in the first time - much more likely.