Am I pregnant or overreacting??

My boyfriend and I have been together for just over 3 years. We have used condoms on and off through out the relationship. He still pulls out even when he has a condom on. I know that he is 100% not ready to be a dad and absolutely doesn't want a kid. Because we live 2 hrs away from each other we don't see each other every weekend. During the week I was ovulating (3 weeks ago) I spent the weekend down at his house. We probably had sex 3 times and I don't remember if condoms were used but the pull out method was for sure used. I noticed last week that I would get suddenly nausus and sometimes puke. Also last Friday I had heart burn for the first time in my life and my nipple were really tender. I took a pregnancy test over the weekend and it came back invalid. Yesterday was supposed to be the day my period started. I am hardly ever late and if I am it usually starts right away the second day. My best friend (due in July) said to take a test again first thing in the morning. I did, but it also came in invalid. I have had scares before, but non like this. Do I need to take another test, or am I just freaking myself out???