I had oral sex with a guy for the first time and now I feel sick... Is it an STD?

I don't know the sexual history of the guy so I'm not sure if he has any STDs or not. Soon after the oral sex I got a headache and the next day I was sneezing and coughing a lot with a headache that comes and goes. My throat doesn't hurt and it looks clear... Actually it feels more like a cold (and a guy I was working with a few days ago did have a cold) but the timing and random headaches worry me a bit... Is it an STD or is my sick co-worker to blame?