What Do Excessive Bleeding When On Depo Shots Indicate?

I m on depo and have been on it for 3 years and sinxe then I ve always had my period every 3 months. For about a year I didn t have sex and after I did which was the last week of November, the week before I got another shot and I was supposed to get my period a couple weeks later but never came. That was December. It s been 14 weeks since then. I waited until January to take a test and it was neg. After I found out it was neg I started working out again and had a gush of blood after my workout and the the day after same workout and had blood after workout. After that I had all his brown discharge and it was so weird. I didn t think anything of it a couple weeks later I decided to go to a clinic to take another test and it was neg. One of my friends thinks I had a miscarriage. Now it s March and I missed another 3 month period and I can feel my uterus and have been for about a month. It s right on top of my pubic bone and I can feel the weight and pressure from it and I ve had a lot of physical changes esp my breasts and emotional changes. I don t know what to do and why I feel my uterus? Could I be pregnant ?