Could it all be in my head?

I missed some days with the pills last month however I kept taking them. I know not the brightest move ever. At the end of June I had my period like normal on the 18th the week before my b-day then the week after on the 25 or so I got another one it lasts less the a week only like 4 days, which is really abnormal for me my cycles always run from Sunday-Sunday or Sunday to Monday. It was also lighter then normal I hardly notices I had it. Over the last few weeks I've been really dizzy and nauseous but I was also going through finals and trying to finish 4 outfits for a fashion show, so I was getting little sleep and little food like every other college student. This past week I've been on break and feeling better but I still have yet to get my period this month. And while Im still feeling a little nauseous every now and then. After a some false alarms I've decided that Im not taking a test until next week if my cycle does not present it's self.

Do you girls think this is all in my head? lately every time i feel slightly off I get the oh you must be pregnant crack so im really starting to think it's only in my head after being let down before. Has anyone else dealt with this?