You are indeed in a tricky situation. Your sexual contacts on 29th, 30th and 31st are very much near the day of the egg formation. Pull out method is one of the most unreliable method of avoiding pregnancy for two reasons. Firstly before actual ejaculation, there is a presemenal discharge which is known to contain some number of sperms. They can fertilize the egg to cause the pregnancy. Secondly, in the heat of the sexual excitement, it is very difficult to plan the withdrawal of the penis well in time. There is always a risk of some semen spilling in to the vagina. You have not mentioned after how many days of missing the period you have started getting the symptoms of nausea and tender breasts. The pregnancy test should be done about 8-10 days after the period is missed. That will tell you correctly whether you are pregnant or not. Even after that also if you are in doubt, you can go for ultrasonography for diagnosis of pregnancy. You seem to be under tremendous stress and upset. Relax and rely on the scientific tests.