Late periods

Okay so I'm 15 and my boyfriend and I have had sex a lot. I just got my period last august for the first time. I usually start my period between the 1st and the 10th of the month. But last month I started the 25th. So would that mean I'm late now? He always pulls out and we usually use condoms but I'm still worried I'm pregnant and I'm not on birth control what do I do? Advice please?!