Could It be possible that I'm pregnant?

I had sex with my boyfriend and the condom pulled off afterwords and was stuck kind of inside of me. not pushed inside kind of inside but laying on top this happened a few weeks ago. I've been having a stuffy dry nose and occasional coughing and I recently threw up this morning. I'm also on depo shot(birth control) and I'm getting the shot again tomorrow. I was fine all morning until I took my vitamin which isn't the best tasting maybe it soured my stomach? I have a disease called Lupus and I cannot be pregnant because it could kill me. Is it possible though?