How likey is this case, please answer its much appriciated

First I will start off by saying; I have never kept track of my period schedule, like exact dates and such. I do not remember getting my period in December, so if I did it would of had to be early December. Point being my period hasn't come for quite awhile. This week, going on two days now, I have been spotting. I took a home pregnancy test the day before the spotting had actually begun, which came out negative. I took the -/+ type pregnancy test, the - was dark at first then faint.

What led me to take the test was because of my period seeming to be absent for quite awhile. Now I have never had sex, nor was I ever sexually active prior to the boyfriend I am with now. I've always had high morals, so I waited till I was in love to do anything intimate. We have engaged in what could be known as mutual masturbation. I have been trying to recall specific incidents that could have led to pregnancy. I know he has in the past after he ejaculated, it would get cleaned up of course, but apparently as the penis goes down a little more excess semen comes out. So after his penis already being back in his boxers, he'd touch the tip to make sure it wasn’t wet enough to have to change underwear. After doing so he'd always wipe his hand off. Mainly we'd cuddle awhile afterwards, and sometimes he'd proceed to enter my vagina with his finger.

I've heard the stories that said how it is possible to get pregnant this way, but how likely is that, should I be as worried as I am? Was the pregnancy test to early since it came before the spotting, though I had already most likely missed my period by then? Also, I am eighteen, could my period still just be irregular? Any help on this matter would be very helpful. I've been quite nauseous lately and I can’t tell if its from worrying or another sign. Thank you very much.