I am not sure if this is true to some extent! But I was talking to a few mums yesterday about their HPT and they mentioned about similar experiences. When they found out they were pregnant with their daughters, they all got pretty early positives around DPO 9-12. When they were pregnant with their sons however, they all got lots of BFNs first before getting their very first faint BFPs round DPO 14 or even much later after they missed their period!
Anyone with DS and DD care to share?