Can you have morning sickness/nausea but still get a negative pregnancy test?

I took 2 pregnancy tests 2-3 weeks after I had (both negative) and friday I took 2 tests and both were positive. I'm now 10 weeks and 3 days pregnant. So what I'm saying is that, the first ones I took came out negative but the one I took friday were positive. I didn't have since then because I had a feeling that I was really pregnant.