What's wrong with my lady parts?

I just had a baby nine months ago and I am on the shot now. The shot has been makin me spot in between periods. Well this time I spotted for a month. Sunday evening I went to the restroom and I was burning really bad. I had like a very thick yellow discharge and it was very red and irritated right in the opening of my vagina. There was like two white spots on one side and like three on the other. Well I went to the doctor on Monday and he done a culture test cause he thought it was herpes. The results came back today and they were negative. Any idea what this could be? It just popped up out of nowhere. The day before it did happen...I had sex with my boyfriend that I've been with for three years and he finished inside of me. But he had just got a tetanus shot because he cut his arm and had to get stitches and was feeling sick and had a fever. Could that have anything to do with my problem since it happened the next day. Another thing I didn't use the bathroom after we were done or take a shower because I fell asleep. So any ideas?