Pregnant? I missed my period last month, and now I'm 2 days late for this cycle?

[Cara]

I've had 3 negative urine tests, but I was told at a Heartbeat center that, based on how far along I would be if I was pregnant, I might not get a positive on a urine test for another month. I'm under a lot of stress lately, but I've never missed a period before because of stress. What are the odds I'm pregnant? Should I get a blood test done, or just wait? My problem is, I'm waiting to start a medication that I can't take if I'm pregnant, so I need to know ASAP