I'm a bit confused about when you had unprotected sex. Was it a week ago? If so, then the pregnancy test wouldn't tell you yet. It takes a few weeks.
Getting sick immediately after you have sex wouldn't have anything to do with the sex. That would probably just be the flu or something. Fertilization doesn't happen for up to a few days after you have sex, and if there is fertilization, the fertilized egg doesn't attach to you for a couple of weeks after, and you wouldn't have a hormonal response (like morning sickness) at least until it was attached to you.
You haven't had a period in three or four months? It sounds like this isn't since you had sex. It sounds like you're just irregular so you can't count on watching for your period to find out if you're pregnant. If I'm wrong, then please correct me. I would wait until a month after you had sex and take another pregnancy test. And of course be more careful in the future. When you went to the doctor, did you talk about birth control? Birth control isn't perfect but it of course makes it much less likely that you'll get pregnant.