Am I pregnant or what could be going on with me?

Hi, ladies. I'm on my 35 cycle day which means I'm a week late on my period as of now. I took 3 different clearblue tests and they all showed negative, but I'm still very worried. I can't have a baby right now as I'm going to college. Me and my SO always use condoms, however there'd been 2 times past month that we used the withdrawal method. We've done it before many times in the past 2 years and never had any problems. Also, in February I began taking microgynon because of very heavy periods, but after a month of continuos bleeding I stopped taking them. My periods are mostly regular with - 2/+2 days. I've been taking vitamin C to induce the period, but only had mild cramps, no bleeding. Also, I've been kinda stressed this past month with job interviews and everything, maybe that's the cause of the delay. What do you think? Could I be pregnant or have a sudden medical condition and should go see a doctor?