Yes, it is possible. Although usually the "pull-out" method works for many it is not guaranteed. Even condoms aren't guaranteed. You may also just have an irregular period. Since it is only the 4th, you're really only like 2 days late. Women can be off by a week or so (early or late) and still be considered normal. I'd recommend taking another pregnancy test in a week, and if you still come up negative but haven't yet gotten your period you should look in to other health problems that could cause this. Also, if you get a lot of exercise you may miss your period, if you are taking medications they may interfere, or if you've been under a lot of stress this may cause irregularities. So, yeah, don't sweat it just yet, but keep your eyes peeled.