Sore boobs

In the past week or two my boobs have been really sore and tender and my nipples have been really sensitive as well. They've even gotten bigger and are heavier, my boyfriend has even commented on it. I'm 15 and a 32G, I've been this big since last year. I don't think it's growing, especially not this fast. I'm also on depo, I'm getting my second shot on Thursday. Could depo be why? I'm just confused. I even took a pregnancy test on Sunday and it came out negative. I don't know why they are doing this.