It can be normal to be a tad later then 'usual' on occasion- especially if you have irregular periods. Even something like stress can cause a period to be late. If you used condoms, it's unlikely that you are pregnant- of course they are not 100% effective, but it's not likely that you are expecting- especially since you have taken a test since being late and gotten a negative result. You can always wait a week and test again, just to put your mind at ease though.