can the doctors urine test be wrong?

Hi i recently took a pregnancy test because i was 2 weeks late for my period....it came back positive! so i went to see my doctor n had a urine test there and it came back negative! i had my blood work done but am waiting for the results! n i have another appointment in a week at the doctor. my stomach is puffed out n very hard! n the last cpl of days ive had a pain in my sides n my ribs. when i told this to my doctor before the urine test he said it was because i was pregnant and my insides were moving up. i really want to be pregnant n ive heard of women thinking themselves pregnant. so i guess my question is can the doctors urine test be wrong? could i really b pregnant?