Might be pregnant?

So my birth control prescription expired and I didn't get around to a doctor appointment to renew it. I've been off it maybe 3 weeks, coincidentally my boyfriend and I have been having a LOT of sex within this time. All of it unprotected, a couple rounds of it every time. Well over the past day or two, I've started to be really nauseous/lightheaded and there's nothing that can really be causing it. My friend brought up that I could be pregnant so I wanted opinions. Any ladies here that can tell me early signs? I'm trying to not get paranoid since I know we can talk our bodies into thinking we are.