I am 12 almost 13 nd i think im pregnant? HELP ME PLEASEEEEEE?

Hey everyone i know this seems awful but i am 12 nd i turn 13 in like 3 weeks.... ok so i think im pregnant...! my boyfriend Chris nd i just got back to gether over spring break nd he cme over my house nd we had sex 2 days in a row nd it was unprotected... he said he was gone pull out but i dont think he pulled out every time he came because he started shaking nd i was like wat is he doin.... Nd BTW he is 15 nd hell be 16 in 8 months... my stomach hurts but ion know wat to do.. i took a test "ike 1 day after we had sex nd it was negative but ima take another one soon cuss i dont think it was accurate... also my mom knows who my bf is ok like i met him like 3 years ago when i was 10 nd i lost my virginity to him then we lost touch because he moved.... nd we just got back together... i dont know if i should tell my moma or not like please help me it will break her heart... i told her wen i first lost my virginity because i was now after 3 long year she finally trusts me nd if im pregnant she want ever trust me