Am I 15 or so weeks pregnant?

Back in march me & my boyfriend decided we wanted a baby. It would be his 2nd. So we tried. I did my research & checked ov days, told him & we went for it.. Waited & as we waited to test I began spotting like a week && a half before my period was due.. Some days it would seem like a regular period & some days it would seem light. It lasted for maybe 3 days & a half. I tested & it was negative. We were disappointed but haven't tried since. In April I began to have what I thought was a period every 3weeks but usually my period is every 28days. I also started having cramps, headaches, crying spells, nausea & dizziness. I took another test still negative. As time past It seem like things got worse, cravings, nausea every time I tried eating, my headaches got worse & they now occur daily. I was weighing 144 & with in the last month I've gained a lot of weight. I'm now 158. My boobs have grown from a 38C to a 40D & my nipples are very tender.. I been having cramps && lower back pains for almost a week. Haven't had any spotting or periods. I can now see my stomach when I look down because its growing past my breast && its always firm sometimes more so in certain places. I'm honestly terrified because I don't know whats going on with me. My boyfriend suggest that I should take a pregnancy test but I feel like it'll just be negative, & I'm not ready to go to the doctor. Does anyone have any words of wisdom? Thanks in advance! Oh and its been a little over 4weeks since Ive had a period. Its late.