could I be really pregnant???

So I have taken about 5 tests.  All say positive. Took a test about a week ago and it was negative. My test says I'm about 4 weeks along? This would be my second child. I have been really sick the last week and the last 2 days cramping backaches a majorly headaches nauseous feeling. Could I really be pregnant? Nothing like this happened with my first. I was about 8 weeks along with her before I found out I was pregnant.