Weight gain, pregnant or just poor diet?

I'm 19 years old and 5'7". So in mid May I weighed 157 lbs.. At my heaviest I've weighed ~168 lbs.. For the last couple of months since school is on summer break I haven't been walking or eating very well. I've also in the last few weeks had unprotected sex with my boyfriend and he has finished in me twice. I've been on the pill for almost 3 years now, and my BF has finished in me countless times with no prgegnancy. He came over to my new apt last weekend and we ate A LOT of junk food and just food in general... At the end of the weekend I weighed myself and was 166 lbs.. Before he came over just a few days before I weighed around 159. Could this be just due to eating junk (like almost a whole pan of brownies, pancakes, a brownie fudge sundae, chicken wings with ranch, steak....) with my BF or could I be pregnant?? I've skipped over my placebo pills for the past 2 months, which I've done many times, so I haven't had my period in almost 3 months. Maybe I'm just feeling weird? Am I being ridiculous? I have no symptoms of being pregnant except my weight gain and I've had nauseous moments the past few days but I also take a medication that sometimes causes dizziness. Am I just being paranoid? And don't worry I've made a drastic change in my eating habits since my BF left.... Lol