Fevers

I recently found out I am pregnant but everything has been way weird with the pregnancy. If I go by the first day of my last period which is what the doctor said to do I'm almost 7 weeks along, according to the blood tests they had done I am only 3-4 weeks along.. If this is correct I literally found out I was pregnant 4 days after I conceived.. Is that even possible? My doctor is treating me like a paranoid new mom but I had q miscarriage in October when I was about this same time period. I've also had a fever off and on that has only been 99-100 and I have been nauseated off and on. I know I sound crazy paranoid but I can't loose another one..