My daughter, who has SWCAH, also did this when she was around 3-4 months. We got the same answer as Misty- I believe it’s caused by withdrawal of maternal hormones, but why it would take 4 months to happen is unknown to me! To be on the safe side, they did take a urine sample and check for a UTI- turned out she didn’t have one and the spotting cleared up in 5-7 days.
Good luck!
Martha