What Does It Mean If My VDRL Is Now Negative But My TPHA Titre Has Risen After Syphilis Treatment?

I got tested for shyplis and my vdrl and toha came positive with 1:16 and thrn i got treatment with 3 pencilin for 3 weeks and Doxycilin pills and then after 2 month i got tested again then vdrl and tpha came reactive with 2:80 so then took doxycilin pills for 2 weeks and then after 2 month i got tested and vdrl came nevative and tpha came 1:640 reactive what does this this mean can somebody tell me