Canker sore, and oral sex

[needsomehelp913]

   I'm new to this board, but I'm extremely worried and I needed to ask this question so make sure I'll be okay.. Here goes nothin'.
   Me and my girlfriend have been dating for a few months, and we're a young, 17 year-old couple.  Last night, we decided to have oral sex.  A few days before, I had gotten a canker.  I get cankers quite often (maybe once a month), and sometimes there's up to three of them in my mouth at once.  I was the one to give the oral sex, and my canker sore had, for the most part, stopped hurting (so I assume it was almost done healing).  It was a pretty large sore at the front of my lip (but still in my mouth), but all of the ones I get are usually like that.  Now, my question is...  Do i have a risk of getting any kind of STD?  My girlfriend is a virgin, and I myself have only had oral with one other girl about a year and a half ago.  I was only doing it for no more than 3 or 4 minutes, and I even brushed my teeth and tried to clean out my mouth afterwards, only hoping it would help (but I doubt it did).
   I hope I can get a reply quickly, so I can either lift this weight off my shoulders, or accept something I never thought would happen to me..