I kept unprotected sex and after that I had menstruation twice in two months. What does that mean ? I've also been experiencing a lot of headaches and I feel like I 'm gonna throw up all the time.

The quick answer is that a pregnancy test can be conducted. The bleeding you had could be an implantation bleeding, which can occur when the embryo implants in the uterus (womb). If you are pregnant, it is most likely that has had an anovulatory menstrual cycle, which means it does not ovulate, which causes hormonal changes and therefore causes abnormal bleeding. There are many causes for this, including stress, weight changes, certain medications, etc..