Maybe your hcg levels are not high enough for a digi to pick up yet, try not to worry too much, give it a day or 2 and test again using fmu.
Test's just vary in the amount of hcg they can detect, and if you have already had bfp's then it's looking good xxx
Hunnie please do not worry!! Read my last threads!! I got a neg on a digi at first too!! and now I have a pos!!! Might still be too soon for the digi to pick up on. Do not give up!!