Slight Crisis, HELP!

Chelsea
Okay ladies! I need some insight! I had a beautiful, smart baby boy in July so he is approaching 8 months. I've been on my birth control since he was about 3 months (I tried to nurse him first). Here's the problem: my period should have been here by Tuesday (2.28) and I haven't had even the slightest symptoms of it coming. Now, I've been working out rigorously to lose the baby weight, and going out on Fridays for drinks. What are the odds that I'm pregnant again? Has anyone else had this scare? I'd love to have another, but not so soon! It's totally possible, but I am hoping you ladies can tell me if I'm freaking out for nothing, or if I should really be concerned. Thank you in advance!