Did you get tested since then? Having no symptoms does not necessarily mean you're free from infection. You can be asymptomatic but still have the infection, and some bacteria/viruses can become dormant for a very long time.
"Can STD's get healed without antibiotics?"
Take note that not all STD's are caused by bacteria, some of them are caused by viruses and parasites, so technically speaking you don't need antibiotics if the STD is not caused by bacteria but still need other treatment. For STDs/STIs that are caused by bacteria (e.g. gonorrhea, chlamydia, mycoplasma genitalium, syphilis) you definitely need antibiotics, it won't go away on its own.