What you describe might be what happened to me with our baby boy several months ago. (He's now just over one year.)
We already had had experience with two girl babies (just like you), but while waiting at the MD's office one afternoon, I was MORTIFIED to find patchy spots in his hair that I somehow had missed!!!!!
At any rate, I was told that this was, indeed cradle cap...which didn't look like cradle cap I'd seen in photos (just never experienced, that's for sure).
On advice, I used a soft bristled brush to 'get out' as much as I could, and started using a different oil product for his hair.
Previous to this, I'd not used too much, because the texture of his hair was different from the girls'. But, indeed, he needed more oil than I was putting in his hair, and it helped considerably. In other words, his scalp was too dry and patchy places had formed.
It was difficult at first to get so much of this out as it seemed that the more I combed and brushed, the more I saw...but eventually, his hair 'cleared'.
Hope this helps in some way...
Sincerely,
Linny