I have been with my boyfriend now for 3 years and every time after we have sex, the following days I have a painful, itchy sensation in my vagina and a yellow discharge. I am on birth control and have very frequent infections including the yellow discharge and the doctor said it is not an STD. We had sex and oral sex recently and I am having the itching and yellow discharge and a little bit of cramping. I had had a cold sore the previous week before we had sex and we avoiding kissing and refrained from sex like we were supposed to. When we had sex my cold sore was completely healed except for one little spot the size of a pencil tip that the scab had not fallen off yet. I understand the risks of cold sores during oral sex but I was certain that it was healed so completely that the risks would be nearly non-existant. I may be paranoid but I am wondering if my symptoms are typical after sex or due to a transfer of the herpes virus?

Your symptoms are not "typical" after sex, so something is going on.

It could be a myriad of things, including a yeast infection (those can be oral as well)

Only a doctor can tell you for sure.