Have you been to the Doctor about the Rash ? If not then i think you should.
Rashes on lower extremities could be a fungal rash that will go away with anti fungal creams.
See a Doctor and get that checked, I’m sure it’s something that will be easily treated.
Yes, the RPR is conclusive at 3 months.
A syphilis rash would also likely be over more of your body than just your lower extremities.
Have you seen a doctor for the rash? If you haven't, you should consider it. Hope it clears soon!