you don't have periods if your pregnant sometimes your cycle can change for no reason. In order for you to be pregnant he would of had to ejaculate inside of you and you would of had to be ovulating. If you are having heavy bleeding then of course you are not pregnant because implantation bleeding last 2 days and is pinkish or brown spot of blood and is followed by cramping but no actual period. I think your mind is playing tricks on you.
Hi, if you have had 2 periods then you are not pregnant. The chances of getting pregnant seems very slim as you did not have sex. If you are really concerned then you should see a doctor but I would assume that your symptoms are stress related.
Your cycle may have changed due to stress of thinking your pregnant or because of the internship, especially if you are away from home. Stress can creep up on us and we don't even realise.