What Causes Dizzy Spells After Stopping Birth Control Pills?

I have been taking the mini pill for 3 months now, my doctor said its good to try different ones to suit me. I had intercourse on the last day of one packet and it was on a friday night, and the next day i came to open my next packet of pills and i had none, i thought i had a packet left so i couldnt get in the doctors because it was wkend and the nearest appointment is 21st feb, i m worried i may be pregnant i am constantly tired, increased appetite, dizzy spells, i have took a test but its negative, its now been 3 weeks since i stopped taking the pills and i havent had a period yet, what else maybe wrong?