Couldn't have an mri scan, they told me because I haven't had my period and I'm definitely not sure if I was pregnant

I'm on day 44 and 15 days late, last week I took a pregnancy test it was negative. They said that they didn't want to take any chances and to re-book and as long as I had a negative test they would re-book.

I was under the impression if I had a negative test I'm definitely not pregnant. I've been drinking, because it was negative.

I thought I would know if I was pregnant by now and that a negative test would be accurate if I used the tests that are for missed periods

I'm kind of concerned now, can you have negative tests and he pregnant