Is It Possible To Have Negative Pregnancy Tests And Still Be Pregnant,and Can Depo Cause False Negatives And Pregnancy Symptoms?

Hi. Question. I started the Depo shot in late April, got another in late July and was due for another by October 31st. I did not get the last shot. I had unprotected sex that day, and a bout a week after using only the withdrawal method. I have not had a period yet, although I bled continuously while on the shot. The only spots I have had have been in the last 2 weeks, one a little pink one day and another day a little pink. The last few months, my bf has said my boobs look bigger. They also are very sore and they hurt when they are squeezed or when I lie on them. When I lie on my stomach it is very uncomfortable. I dare to say I can feel something moving around.I have nausea, and terrible gas and headaches. I have been craving foods and eat all day. I have all the symptoms of pregnancy, but I have taken 3 hpts which all said negative. Is it possible to have negative pregnancy tests and still be pregnant? Can the depo cause these false negatives or does it cause these symptoms?