There is no way to tell what it was without testing. And since you have cleared up, there is nothing to test. But it still wouldn't hurt to give yourself a peace of mind by testing.
Syphilis would respond to doxycycline but not the others. However, it is very rare in the U.S., and lesions usually appear on the shaft, not the pubic area.
If it were syphilis, you may not necessarily have received a curative dose of doxycycline, so you might want to get a blood test to be sure that you don't have it. But as I said, I doubt if what you have described were syphilis lesions.