Birth Control

Last July 2018, I got on Depo for the first time. The first 3 months while being on Depo I was spotting the whole time. The second time I got the Shot I was spotting for a week but not my actual period. The 3rd time getting the Shot I didn’t bleed at all. After my 3rd I didn’t go back to get the shot, I lasted 3 months without any Birth control and still didn’t get my period. Recently my Doctor told me to get on the pill it’s been 3 weeks since im on the pill and my breast really hurts/ swollen and I’ve been waking up with headaches but still haven’t gotten my period, and I have unprotected sex, and have taken a few pregnancy test and it comes out negative. Honestly I haven’t gotten my period in about 8 months. My Doctor says it’s because of depo, but I should get my period soon. Im worried !!!