Thanks for your question and concern as this infection is very common in human being which is caused during sexual intercourse, as you need to know about the bacteria which causes this infection. STIs is a sexually transmitted infection  which is transmitted during unprotected sex and is advisable to go for a protected sex as it prevents you from infection. In the market there are various types of protections available for which you can go for. Using condom as well as pill is the best way of protection as it is called dual method in which the chances of STIs and pregnancy are very less. The chance of Knoppix is not there as this infection is the transmitted disease which is caused during unprotected sexual intercourse. As you have mentioned that you and your boyfriend went for the checkup and you both were given all clear but I would suggest you to go for a full screening because somehow this infection does not show their symptoms in many cases. You must need to know about what type of bacteria it is and which bacteria has caused this symptoms because after knowing about the symptoms you can go for a treatment .

According to me I would suggest you both to go for a recheckup and advise you to go for a protected sex during sexual intercourse. Take care.