Ok soo a little help would be awesome..?

Well I haven't had my period since May 6th lol and that is a little weird. My period is like usually regular. Nothing has changed in my life at all so I don't know what is going on. I had a doctors appointment today but I missed it due to traffic but I was just wondering if anyone has any ideas of whats going on. Oh and it's not menopause lol someone suggested that before but I'm only 18 and pretty sure that's impossible. The only symptoms I've been having are 24/7 nautiousness lol and for some reason lower back pain. I took pregnancy tests like two or three weeks ago and they were negative. Oh and btw I did have unprotected in May so I guess pregnancy is not to far fetched. I just need some personal opinions : ]