I really think I may be pregnant at 15 :/?

I started my periods just over a month ago and they were all ok, maybe a little heavy but not too severe. and about 2-3 weeks later I had sex for the first time with my boyfriend, unprotected (stupidly).I have not had a period since but I know when you first start your periods they can be irregular and stuff so I'm not to worried. But I have been feeling rather odd ... Grumpy for no reason, lightheaded, dizzy and confused... sometimes feeling a little sick. Help? :/ I'm really scared x