Negative HPT positive blood test?

my periods are regular...every 29 days on the dot for 4 days (heavy the first 3). My and my fiance are ttc. My period was due on 5/23. On 5/21 I had pink tinged cm (that I never have had before). The day of my period...NOTHING. At 1am the next morning, I began to bleed. Heavy enough to need a tampon, but not heavy enough to fill one. Did not fill one tampon the entire day (extremely abnormal). My "period" was gone by that evening. The next day I had brown discharge. I had PMS symptoms to the max... EXTREME FATIGUE, DIZZYNESS, LIGHTHEADEDNESS, CRAVINGS, ETC), I took a hpt this morning (5/21) and it was negative. My doc wants me to take a blood test today. Could I really be pregnant. My cycle has never been this off. We have a 4 year old son and with him I had no symtoms. We are really trying to have another baby. We BD'd alot this month... crossing my fingers.