Once in a Blue Moon, and we've had one this year, a girl gets pregnant by 'dry humping.' In most cases, the guy shoots his load adn the girl get exposed directly, within a few minutes, for this to happen. It can happen if his semen touches your undergarments, and then swim into you via the moisture you secrete to have intercourse. You must be in your fertile days for this to happen. Trust me, it is really a freak accident.
It is really simple. If you have a period, you're 'washed clean' and have really, really low odds of being pregnant. Pregnancy tests test for hormones in your urine, or blood, and cannot test positive unless your body is reacting to a pregnancy, or you have done something that simulates a pregnancy, like some drugs can do. In short, it's hard to get pregnant to being with (ask any woman trying), unless you just really screw up. It's like a lottery. Most people who win don't need the money that bad. Most girls don't need the baby, and just hit that one lucky number to win. I know it by the name Murphy's Law.
I know this won't go over well, but may I suggest getting on the pill? If you do, and don't do anything, then you'll know you're safe. If you do go all the way, you'll still be safer than the stress you're going through now, not protected. You see, the stress and worry over all of this is worse than being pregnant and what naturally happens. And, for the cost of all the tests, you can be on the pill for years. Ask your mother, but she may agree with me. The cost is less than the stress that eats away at you and us.
Hope things work out. And you may suggest he wraps it in a condom anyway, just be extra safe. I would hate to see you with grey hair and not even out of your teens. Yes, joking, but you know what I mean. Take care, ok?