I think it's probably just your body getting used to the birth control again. It's very unlikely to start having symptoms of pregnancy just 2 days after sex. I am very sensitive in my pregnancy and am feeling literally everything, but i didn't start having true pregnancy symptoms for almost 3 weeks after sex.
so of course, do the whole taking of a test if you miss your period, but remember that you've just started back on the pill so your cycle may be off for a month or so anyway, but i think you're probably ok
