Scared

So me and my boyfriend have sex about once a week sometimes more often and I let him cum inside me most of the time. I have been late on my period for the last few times. I'm only 15 so it could just be my body getting use to the change in things but I'm scared it could be a weird pregnancy thing. So I just wanna know if anyone has any opinions on how I should hadle this or if you know what it is let me know. I just feel like I am sometimes but I eventually get my period like 4-7 days after I'm suppose to get it. Idk what it is and just wanna check that nothing is wrong with me and it's just puberty.