Help! please ! , im think i might be preagnant but aint sure can someone help please ! ): , im really hoping ?

Well I'm 17 and my boyfriend and I have been having unprotected sex he had *** in me 17,19,21,23, & 25 , and on april 25 I had my period , but its weird I only lasted 3 days and than it was all brownish , I usually last about 8 days with it, for me that aint normal since it had never happen before ,I have taken 2 preagnacy test , the first one it was negative but like I could see the other line but really light , than the next week I took another one and it was negative ): , we really want a bby its just that we don't know what's going on and I have been having major headaches but then they go away and than come back, last week when , I took a shower and saw darkish blue on my breast (exactly like veins ) people say its early preagnancy , but feww days pass and there gone , but I sometimes feel a sharp pain on my right breast, and lower my stomach mostly on the right but also on the left but why am I getting negative. On the preagnacy test,I have felt really tired, bloated , get full really fast,nausea, and of course headaches .were really trying to have a family I don't actually know when I ovulate my cycle is 28 , he has *** also in me 8, 10, and we might try it on the fourthteen since people always say that's when almost a lot of people ovulate that day , I don't know what's wrong with me can someone please help me ?. , I don't actually know when I ovulate can someone help please ?