Went to the doctors and got a pregnancy test done and it came back negative

I missed my period and today is day 4 and I went to the doctors yesterday to get a check up and they did a pregnancy test but it came back negative. I've never really had this happen before but 1 time. I texted my doctor and asked her but she did not answer back yet because she is working. I don't know what to do or what to say my boyfriend doesn't know I got the test done. I keep getting these cramps where I would get them for my period. I keep checking for blood but there doesn't seem to be any. I need some help on what to do because I don't have any money to go get a test to take one. I'm very anxious to see if I am or not but I don't know how to handle missing my period.