i am late for my period so i have took 4 pregnacy test?

[Lisa J]

and they have all come back negative but i didnt know the exact date of my periods as they are irregular due to having a baby 12 month ago and then been on the depo injection for 2 months but stopped having the injection in january and have always had a period untill now so i took 4 test last saturady well i took 2 and then another 2 through week buy now i think that i might have took them too earley does anyone know if the TESCO HOME BRAND can be took a 5 days earley thanks