I got rx azelaic acid from a dermatologist to help fade mine. I'm still breastfeeding, so that's about the strongest thing I can use, but paired with vitamin C, it's supposed to rival retinol in its effectiveness. I'd highly suggest seeing a dermatologist, they'll be able to go over what options are available to you
I feel you I have a patch on my forehead as well and found nothing to help yet :(
I had it too and tried different things, nothing worked, just continued to use spf50 outside and after 2 years it's almost gone but still a little visible.
Might be a bit difficult to treat if you are pregnant because your hormones and skin will continue to change. Do you use any exfoliants? AHA, lactic acids? That might help with your routine.