It is important that you understand that even though you and your boyfriend have not actually had intercourse, engaging in oral sex- particularly unprotected oral sex- is not without risk and not something that should be taken lightly.
 

Although you cannot get pregnant through straight oral sex as long as the genitals do not come in contact with each other and there is no exchange of semen, it is still risky for STDs. Having oral sex does not protect against herpes and other sexually transmitted diseases. The membranes in the mouth are thin and easily penetrated. There is also the chance that you or your partner can have open sores or cuts in the mouth region and not know about them. It is important to get into the habit of using some form of protection. Condoms work well when performing oral sex on a man.
 

On the other hand, it could be as simple as your boyfriend may have ate something spicy or peppery and the residue of it was on his tongue when he licked your privates.