Hi there - pulling out is not an effective method of birth control at all. Pre-cum still has sperm that can result in pregnancy, and depending on what's going on with your cycle, you could have been in your fertile window on April 7.
The menstrual cycle, particularly in young women, can be easily affected by changes in lifestyle, such as level of exercise, diet, and sleep. So, the delay in your period may be influenced by those factors. If you still haven't seen your period, you should take a pregnancy test ASAP, since a pregnancy test is the only way to know for sure if you are pregnant or not.
Let us know how it goes for you.