Hi there - you definitely had a false positive. Pregnancy is known to cause false positives. The P24 is a confirmation test, and since that was negative, you definitely don't have HIV.
Excuse me - I wasn't 100% focused here. The P24 is an antigen detection test, which would detect a fairly new infection, not a long-existing infection. The doctor may order a follow-up RNA test, but it will be negative since you haven't had a risk for HIV, and you test regularly.
This is definitely a false positive, and I wouldn't be concerned about it at all.