birth control ruined me???

My periods have been pretty irregular ever since I got off of my depo shot. (ive been off it for a year and a half)In the past 2 months my and my boyfriend haven't used any contraceptive. For the past 2 weeks I've been feeling nauseous but I've taken about 4 tests in the past 3 weeks and all negative?? I have a toddler and I know what it feels like to be pregnant and I swear I feel pregnant! I had a period about 3 weeks ago though... I just don't know what to do other than go to the doctor. I have heard horror stories about how depo shot ruins your body and some women cant get pregnant anymore because of it. I hope thats not the case for me.... I even feel sick at this very moment. Just slight nausea and mood swings like crazy. Any advice??