Iirc first response early result has a detection level of 25miu/l while the clear blue easy digital has a detection level of 50miu/l meaning the first response can detect as little as half the amount the clear blue can.
Also blue dye tests (as what the strip in the clear blue is) are not as accurate as the pink dye tests (as found in the first response).
It is possible that the first test gave an evap line but evaps are not pink (usually more greyish or clear) and not as wide as the control line and do not show up within the time limit.
False negatives are common
false positives are very very rare
test again in a few days when your level of hcg has had a chance to increase.
If you still get a negative then see your doctor for a blood test.
It is also possible to have a chemical pregnancy that shows up faint on a pregnancy test but the lines do not get darker over a period of several days and then to get a negative test.
It's not common but it is possible.