Well to MDC! My short answer is no, it's way too soon to be experiencing pregnancy symptoms if the only sex you had was 3 days ago. Symptoms due to pregnancy would show up after implantation occurs, which would be 6-12 days past ovulation (DPO), most likely 8-10 DPO. At most you could be 4 DPO today if you caught the egg the day after ovulation. Most likely what you are experiencing is due to hormonal fluctuations associated with ovulation (assuming this is the right time of your cycle to be ovulating). Stinging in the vaginal area could be due to irritation or infection. Keep an eye on your vaginal secretions to see if there is any sign of infection. I personally have not heard of vaginal stinging as a pregnancy symptom. Keep us posted!