Trying to concieve

this month I really thought i was pregnant!!! I had all the signs from swollen tender breasts to a metallicy spoon like tast in my mouth and of course no period. but all my home tests were negative so i went in and had a blood test done and it was negative!!! The weird thing is I truly still feel pregnant!!! I have even been getting morning ( all day) sickness whenever I feel the least bit hungry and still have not had my period. does anyone know how far along you need to be for a blood test to show hcg hormones? maybe i just tested to soon i mean my periods are not always 100% regular all the time!