You should determine about when you had your last period (ovulation often occurs between day 10-17-everyone is different). If you have a regular cycle which is about 28 days, anticipate when your due for your next period. There are several pregnancy tests that claim to provide early results, up to six days prior to your period, however the results indicate a small percenatge of accuracy when performed early-accuracy increases closer to your due date.
There are other resources such as planned parenthood, community women's health organizations, or your family doctor that can perform a serum test.
You can test as soon as two, preferably three, weeks after having sex. It takes time for the hormone hCG, made by the fetus, to rise high enough to be detected. If you do test, use your first morning urine - wake up pee - for the best accuracy.
It's too early for any signs of pregnancy. You CAN have pain from just having sex.
Hope it helps.