Just wanted to add something funny and I guess i'm detracting from the thread!
When I went for my 20 week scan with ds the radiographer (?) said 'Even though the hands are in the way, i'm pretty sure this is a boy'. I asked how she knew and she said 'Because he's playing with his penis. Oh look, there you go. Yep definitely a boy'. She said they start playing with them very early. Can't say if he had an erection then but it was a favoured womb toy .
OP if it worries you ask the gp next time you go in. Just nice to have any worries addressed early.